Debezium User Guide
For use with Debezium 1.7
Abstract
Preface
Debezium is a set of distributed services that capture row-level changes in your databases so that your applications can see and respond to those changes. Debezium records all row-level changes committed to each database table. Each application reads the transaction logs of interest to view all operations in the order in which they occurred.
This guide provides details about using the following Debezium topics:
- Chapter 1, High level overview of Debezium
- Chapter 2, Required custom resource upgrades
- Chapter 3, Debezium connector for Db2
- Chapter 4, Debezium connector for MongoDB
- Chapter 5, Debezium connector for MySQL
- Chapter 6, Debezium Connector for Oracle (Technology Preview)
- Chapter 7, Debezium connector for PostgreSQL
- Chapter 8, Debezium connector for SQL Server
- Chapter 9, Monitoring Debezium
- Chapter 10, Debezium logging
- Chapter 11, Configuring Debezium connectors for your application
- Chapter 12, Applying transformations to modify messages exchanged with Apache Kafka
Making open source more inclusive
Red Hat is committed to replacing problematic language in our code, documentation, and web properties. We are beginning with these four terms: master, slave, blacklist, and whitelist. Because of the enormity of this endeavor, these changes will be implemented gradually over several upcoming releases. For more details, see our CTO Chris Wright’s message.
Chapter 1. High level overview of Debezium
Debezium is a set of distributed services that capture changes in your databases. Your applications can consume and respond to those changes. Debezium captures each row-level change in each database table in a change event record and streams these records to Kafka topics. Applications read these streams, which provide the change event records in the same order in which they were generated.
More details are in the following sections:
1.1. Debezium Features
Debezium is a set of source connectors for Apache Kafka Connect. Each connector ingests changes from a different database by using that database’s features for change data capture (CDC). Unlike other approaches, such as polling or dual writes, log-based CDC as implemented by Debezium:
- Ensures that all data changes are captured.
- Produces change events with a very low delay while avoiding increased CPU usage required for frequent polling. For example, for MySQL or PostgreSQL, the delay is in the millisecond range.
- Requires no changes to your data model, such as a "Last Updated" column.
- Can capture deletes.
- Can capture old record state and additional metadata such as transaction ID and causing query, depending on the database’s capabilities and configuration.
Five Advantages of Log-Based Change Data Capture is a blog post that provides more details.
Debezium connectors capture data changes with a range of related capabilities and options:
- Snapshots: optionally, an initial snapshot of a database’s current state can be taken if a connector is started and not all logs still exist. Typically, this is the case when the database has been running for some time and has discarded trannsaction logs that are no longer needed for transaction recovery or replication. There are different modes for performing snapshots, including support for incremental snapshots, which can be triggered at connector runtime. For more details, see the documentation for the connector that you are using.
- Filters: you can configure the set of captured schemas, tables and columns with include/exclude list filters.
- Masking: the values from specific columns can be masked, for example, when they contain sensitive data.
- Monitoring: most connectors can be monitored by using JMX.
- Ready-to-use single message transformations (SMTs) for message routing, filtering, event flattening, and more. For more information about the SMTs that Debezium provides, see Applying transformations to modify messages exchanged with Apache Kafka.
The documentation for each connector provides details about the connectors features and configuration options.
1.2. Description of Debezium architecture
You deploy Debezium by means of Apache Kafka Connect. Kafka Connect is a framework and runtime for implementing and operating:
- Source connectors such as Debezium that send records into Kafka
- Sink connectors that propagate records from Kafka topics to other systems
The following image shows the architecture of a change data capture pipeline based on Debezium:
As shown in the image, the Debezium connectors for MySQL and PostgresSQL are deployed to capture changes to these two types of databases. Each Debezium connector establishes a connection to its source database:
-
The MySQL connector uses a client library for accessing the
binlog
. - The PostgreSQL connector reads from a logical replication stream.
Kafka Connect operates as a separate service besides the Kafka broker.
By default, changes from one database table are written to a Kafka topic whose name corresponds to the table name. If needed, you can adjust the destination topic name by configuring Debezium’s topic routing transformation. For example, you can:
- Route records to a topic whose name is different from the table’s name
- Stream change event records for multiple tables into a single topic
After change event records are in Apache Kafka, different connectors in the Kafka Connect eco-system can stream the records to other systems and databases such as Elasticsearch, data warehouses and analytics systems, or caches such as Infinispan. Depending on the chosen sink connector, you might need to configure Debezium’s new record state extraction transformation. This Kafka Connect SMT propagates the after
structure from Debezium’s change event to the sink connector. This is in place of the verbose change event record that is propagated by default.
Chapter 2. Required custom resource upgrades
Debezium is a Kafka connector plugin that is deployed to an Apache Kafka cluster that runs on AMQ Streams on OpenShift. To prepare for OpenShift CRD v1
, in the current version of AMQ Streams the required version of the custom resource definitions (CRD) API is now set to v1beta2
. The v1beta2
version of the API replaces the previously supported v1beta1
and v1alpha1
API versions. Support for the v1alpha1
and v1beta1
API versions is now deprecated in AMQ Streams. Those earlier versions are now removed from most AMQ Streams custom resources, including the KafkaConnect and KafkaConnector resources that you use to configure Debezium connectors.
The CRDs that are based on the v1beta2
API version use the OpenAPI structural schema. Custom resources based on the superseded v1alpha1 or v1beta1 APIs do not support structural schemas, and are incompatible with the current version of AMQ Streams. Before you upgrade to AMQ Streams2.0, you must upgrade existing custom resources to use API version kafka.strimzi.io/v1beta2
. You can upgrade custom resources any time after you upgrade to AMQ Streams 1.7. You must complete the upgrade to the v1beta2 API before you upgrade to AMQ Streams2.0 or newer.
To facilitate the upgrade of CRDs and custom resources, AMQ Streams provides an API conversion tool that automatically upgrades them to a format that is compatible with v1beta2
. For more information about the tool and for the complete instructions about how to upgrade AMQ Streams, see Deploying and Upgrading AMQ Streams on OpenShift.
The requirement to update custom resources applies only to Debezium deployments that run on AMQ Streams on OpenShift. The requirement does not apply to Debezium on Red Hat Enterprise Linux
Chapter 3. Debezium connector for Db2
Debezium’s Db2 connector can capture row-level changes in the tables of a Db2 database. For information about the Db2 Database versions that are compatible with this connector, see the Debezium Supported Configurations page.
This connector is strongly inspired by the Debezium implementation of SQL Server, which uses a SQL-based polling model that puts tables into "capture mode". When a table is in capture mode, the Debezium Db2 connector generates and streams a change event for each row-level update to that table.
A table that is in capture mode has an associated change-data table, which Db2 creates. For each change to a table that is in capture mode, Db2 adds data about that change to the table’s associated change-data table. A change-data table contains an entry for each state of a row. It also has special entries for deletions. The Debezium Db2 connector reads change events from change-data tables and emits the events to Kafka topics.
The first time a Debezium Db2 connector connects to a Db2 database, the connector reads a consistent snapshot of the tables for which the connector is configured to capture changes. By default, this is all non-system tables. There are connector configuration properties that let you specify which tables to put into capture mode, or which tables to exclude from capture mode.
When the snapshot is complete the connector begins emitting change events for committed updates to tables that are in capture mode. By default, change events for a particular table go to a Kafka topic that has the same name as the table. Applications and services consume change events from these topics.
The connector requires the use of the abstract syntax notation (ASN) libraries, which are available as a standard part of Db2 for Linux. To use the ASN libraries, you must have a license for IBM InfoSphere Data Replication (IIDR). You do not have to install IIDR to use the ASN libraries.
Information and procedures for using a Debezium Db2 connector is organized as follows:
- Section 3.1, “Overview of Debezium Db2 connector”
- Section 3.2, “How Debezium Db2 connectors work”
- Section 3.3, “Descriptions of Debezium Db2 connector data change events”
- Section 3.4, “How Debezium Db2 connectors map data types”
- Section 3.5, “Setting up Db2 to run a Debezium connector”
- Section 3.6, “Deployment of Debezium Db2 connectors”
- Section 3.7, “Monitoring Debezium Db2 connector performance”
- Section 3.8, “Managing Debezium Db2 connectors”
- Section 3.9, “Updating schemas for Db2 tables in capture mode for Debezium connectors”
3.1. Overview of Debezium Db2 connector
The Debezium Db2 connector is based on the ASN Capture/Apply agents that enable SQL Replication in Db2. A capture agent:
- Generates change-data tables for tables that are in capture mode.
- Monitors tables in capture mode and stores change events for updates to those tables in their corresponding change-data tables.
The Debezium connector uses a SQL interface to query change-data tables for change events.
The database administrator must put the tables for which you want to capture changes into capture mode. For convenience and for automating testing, there are Debezium user-defined functions (UDFs) in C that you can compile and then use to do the following management tasks:
- Start, stop, and reinitialize the ASN agent
- Put tables into capture mode
- Create the replication (ASN) schemas and change-data tables
- Remove tables from capture mode
Alternatively, you can use Db2 control commands to accomplish these tasks.
After the tables of interest are in capture mode, the connector reads their corresponding change-data tables to obtain change events for table updates. The connector emits a change event for each row-level insert, update, and delete operation to a Kafka topic that has the same name as the changed table. This is default behavior that you can modify. Client applications read the Kafka topics that correspond to the database tables of interest and can react to each row-level change event.
Typically, the database administrator puts a table into capture mode in the middle of the life of a table. This means that the connector does not have the complete history of all changes that have been made to the table. Therefore, when the Db2 connector first connects to a particular Db2 database, it starts by performing a consistent snapshot of each table that is in capture mode. After the connector completes the snapshot, the connector streams change events from the point at which the snapshot was made. In this way, the connector starts with a consistent view of the tables that are in capture mode, and does not drop any changes that were made while it was performing the snapshot.
Debezium connectors are tolerant of failures. As the connector reads and produces change events, it records the log sequence number (LSN) of the change-data table entry. The LSN is the position of the change event in the database log. If the connector stops for any reason, including communication failures, network problems, or crashes, upon restarting it continues reading the change-data tables where it left off. This includes snapshots. That is, if the snapshot was not complete when the connector stopped, upon restart the connector begins a new snapshot.
3.2. How Debezium Db2 connectors work
To optimally configure and run a Debezium Db2 connector, it is helpful to understand how the connector performs snapshots, streams change events, determines Kafka topic names, and handles schema changes.
Details are in the following topics:
- Section 3.2.1, “How Debezium Db2 connectors perform database snapshots”
- Section 3.2.2, “How Debezium Db2 connectors read change-data tables”
- Section 3.2.3, “Default names of Kafka topics that receive Debezium Db2 change event records”
- Section 3.2.4, “About the Debezium Db2 connector schema change topic”
- Section 3.2.5, “Debezium Db2 connector-generated events that represent transaction boundaries”
3.2.1. How Debezium Db2 connectors perform database snapshots
Db2`s replication feature is not designed to store the complete history of database changes. Consequently, when a Debezium Db2 connector connects to a database for the first time, it takes a consistent snapshot of tables that are in capture mode and streams this state to Kafka. This establishes the baseline for table content.
By default, when a Db2 connector performs a snapshot, it does the following:
-
Determines which tables are in capture mode, and thus must be included in the snapshot. By default, all non-system tables are in capture mode. Connector configuration properties, such as
table.exclude.list
andtable.include.list
let you specify which tables should be in capture mode. -
Obtains a lock on each of the tables in capture mode. This ensures that no schema changes can occur in those tables during the snapshot. The level of the lock is determined by the
snapshot.isolation.mode
connector configuration property. - Reads the highest (most recent) LSN position in the server’s transaction log.
- Captures the schema of all tables that are in capture mode. The connector persists this information in its internal database history topic.
- Optional, releases the locks obtained in step 2. Typically, these locks are held for only a short time.
At the LSN position read in step 3, the connector scans the capture mode tables as well as their schemas. During the scan, the connector:
- Confirms that the table was created before the start of the snapshot. If it was not, the snapshot skips that table. After the snapshot is complete, and the connector starts emitting change events, the connector produces change events for any tables that were created during the snapshot.
- Produces a read event for each row in each table that is in capture mode. All read events contain the same LSN position, which is the LSN position that was obtained in step 3.
- Emits each read event to the Kafka topic that has the same name as the table.
- Records the successful completion of the snapshot in the connector offsets.
3.2.1.1. Ad hoc snapshots
The use of ad hoc snapshots is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service-level agreements (SLAs) and might not be functionally complete; therefore, Red Hat does not recommend implementing any Technology Preview features in production environments. This Technology Preview feature provides early access to upcoming product innovations, enabling you to test functionality and provide feedback during the development process. For more information about support scope, see Technology Preview Features Support Scope.
By default, a connector runs an initial snapshot operation only after it starts for the first time. Following this initial snapshot, under normal circumstances, the connector does not repeat the snapshot process. Any future change event data that the connector captures comes in through the streaming process only.
However, in some situations the data that the connector obtained during the initial snapshot might become stale, lost, or incomplete. To provide a mechanism for recapturing table data, Debezium includes an option to perform ad hoc snapshots. The following changes in a database might be cause for performing an ad hoc snapshot:
- The connector configuration is modified to capture a different set of tables.
- Kafka topics are deleted and must be rebuilt.
- Data corruption occurs due to a configuration error or some other problem.
You can re-run a snapshot for a table for which you previously captured a snapshot by initiating a so-called ad-hoc snapshot. Ad hoc snapshots require the use of signaling tables. You initiate an ad hoc snapshot by sending a signal request to the Debezium signaling table.
When you initiate an ad hoc snapshot of an existing table, the connector appends content to the topic that already exists for the table. If a previously existing topic was removed, Debezium can create a topic automatically if automatic topic creation is enabled.
Ad hoc snapshot signals specify the tables to include in the snapshot. The snapshot can capture the entire contents of the database, or capture only a subset of the tables in the database.
You specify the tables to capture by sending an execute-snapshot
message to the signaling table. Set the type of the execute-snapshot
signal to incremental
, and provide the names of the tables to include in the snapshot, as described in the following table:
Field | Default | Value |
---|---|---|
|
|
Specifies the type of snapshot that you want to run. |
| N/A |
An array that contains the fully-qualified names of the table to be snapshotted. |
Triggering an ad hoc snapshot
You initiate an ad hoc snapshot by adding an entry with the execute-snapshot
signal type to the signaling table. After the connector processes the message, it begins the snapshot operation. The snapshot process reads the first and last primary key values and uses those values as the start and end point for each table. Based on the number of entries in the table, and the configured chunk size, Debezium divides the table into chunks, and proceeds to snapshot each chunk, in succession, one at a time.
Currently, the execute-snapshot
action type triggers incremental snapshots only. For more information, see Incremental snapshots.
3.2.1.2. Incremental snapshots
The use of incremental snapshots is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service-level agreements (SLAs) and might not be functionally complete; therefore, Red Hat does not recommend implementing any Technology Preview features in production environments. This Technology Preview feature provides early access to upcoming product innovations, enabling you to test functionality and provide feedback during the development process. For more information about support scope, see Technology Preview Features Support Scope.
To provide flexibility in managing snapshots, Debezium includes a supplementary snapshot mechanism, known as incremental snapshotting. Incremental snapshots rely on the Debezium mechanism for sending signals to a Debezium connector.
In an incremental snapshot, instead of capturing the full state of a database all at once, as in an initial snapshot, Debezium captures each table in phases, in a series of configurable chunks. You can specify the tables that you want the snapshot to capture and the size of each chunk. The chunk size determines the number of rows that the snapshot collects during each fetch operation on the database. The default chunk size for incremental snapshots is 1 KB.
As an incremental snapshot proceeds, Debezium uses watermarks to track its progress, maintaining a record of each table row that it captures. This phased approach to capturing data provides the following advantages over the standard initial snapshot process:
- You can run incremental snapshots in parallel with streamed data capture, instead of postponing streaming until the snapshot completes. The connector continues to capture near real-time events from the change log throughout the snapshot process, and neither operation blocks the other.
- If the progress of an incremental snapshot is interrupted, you can resume it without losing any data. After the process resumes, the snapshot begins at the point where it stopped, rather than recapturing the table from the beginning.
-
You can run an incremental snapshot on demand at any time, and repeat the process as needed to adapt to database updates. For example, you might re-run a snapshot after you modify the connector configuration to add a table to its
table.include.list
property.
Incremental snapshot process
When you run an incremental snapshot, Debezium sorts each table by primary key and then splits the table into chunks based on the configured chunk size. Working chunk by chunk, it then captures each table row in a chunk. For each row that it captures, the snapshot emits a READ
event. That event represents the value of the row when the snapshot for the chunk began.
As a snapshot proceeds, it’s likely that other processes continue to access the database, potentially modifying table records. To reflect such changes, INSERT
, UPDATE
, or DELETE
operations are committed to the transaction log as per usual. Similarly, the ongoing Debezium streaming process continues to detect these change events and emits corresponding change event records to Kafka.
How Debezium resolves collisions among records with the same primary key
In some cases, the UPDATE
or DELETE
events that the streaming process emits are received out of sequence. That is, the streaming process might emit an event that modifies a table row before the snapshot captures the chunk that contains the READ
event for that row. When the snapshot eventually emits the corresponding READ
event for the row, its value is already superseded. To ensure that incremental snapshot events that arrive out of sequence are processed in the correct logical order, Debezium employs a buffering scheme for resolving collisions. Only after collisions between the snapshot events and the streamed events are resolved does Debezium emit an event record to Kafka.
Snapshot window
To assist in resolving collisions between late-arriving READ
events and streamed events that modify the same table row, Debezium employs a so-called snapshot window. The snapshot windows demarcates the interval during which an incremental snapshot captures data for a specified table chunk. Before the snapshot window for a chunk opens, Debezium follows its usual behavior and emits events from the transaction log directly downstream to the target Kafka topic. But from the moment that the snapshot for a particular chunk opens, until it closes, Debezium performs a de-duplication step to resolve collisions between events that have the same primary key..
For each data collection, the Debezium emits two types of events, and stores the records for them both in a single destination Kafka topic. The snapshot records that it captures directly from a table are emitted as READ
operations. Meanwhile, as users continue to update records in the data collection, and the transaction log is updated to reflect each commit, Debezium emits UPDATE
or DELETE
operations for each change.
As the snapshot window opens, and Debezium begins processing a snapshot chunk, it delivers snapshot records to a memory buffer. During the snapshot windows, the primary keys of the READ
events in the buffer are compared to the primary keys of the incoming streamed events. If no match is found, the streamed event record is sent directly to Kafka. If Debezium detects a match, it discards the buffered READ
event, and writes the streamed record to the destination topic, because the streamed event logically supersede the static snapshot event. After the snapshot window for the chunk closes, the buffer contains only READ
events for which no related transaction log events exist. Debezium emits these remaining READ
events to the table’s Kafka topic.
The connector repeats the process for each snapshot chunk.
Triggering an incremental snapshot
Currently, the only way to initiate an incremental snapshot is to send an ad hoc snapshot signal to the signaling table on the source database. You submit signals to the table as SQL INSERT
queries. After Debezium detects the change in the signaling table, it reads the signal, and runs the requested snapshot operation.
The query that you submit specifies the tables to include in the snapshot, and, optionally, specifies the kind of snapshot operation. Currently, the only valid option for snapshots operations is the default value, incremental
.
To specify the tables to include in the snapshot, provide a data-collections
array that lists the tables, for example,{"data-collections": ["public.MyFirstTable", "public.MySecondTable"]}
The data-collections
array for an incremental snapshot signal has no default value. If the data-collections
array is empty, Debezium detects that no action is required and does not perform a snapshot.
Prerequisites
- A signaling data collection exists on the source database and the connector is configured to capture it.
-
The signaling data collection is specified in the
signal.data.collection
property.
Procedure
Send a SQL query to add the ad hoc incremental snapshot request to the signaling table:
INSERT INTO _<signalTable>_ (id, type, data) VALUES (_'<id>'_, _'<snapshotType>'_, '{"data-collections": ["_<tableName>_","_<tableName>_"],"type":"_<snapshotType>_"}');
For example,
INSERT INTO myschema.debezium_signal (id, type, data) VALUES('ad-hoc-1', 'execute-snapshot', '{"data-collections": ["schema1.table1", "schema2.table2"],"type":"incremental"}');
The values of the
id
,type
, anddata
parameters in the command correspond to the fields of the signaling table.The following table describes the these parameters:
Table 3.2. Descriptions of fields in a SQL command for sending an incremental snapshot signal to the signaling table Value Description myschema.debezium_signal
Specifies the fully-qualified name of the signaling table on the source database
ad-hoc-1
The
id
parameter specifies an arbitrary string that is assigned as theid
identifier for the signal request.
Use this string to identify logging messages to entries in the signaling table. Debezium does not use this string. Rather, during the snapshot, Debezium generates its ownid
string as a watermarking signal.execute-snapshot
Specifies
type
parameter specifies the operation that the signal is intended to trigger.
data-collections
A required component of the
data
field of a signal that specifies an array of table names to include in the snapshot.
The array lists tables by their fully-qualified names, using the same format as you use to specify the name of the connector’s signaling table in thesignal.data.collection
configuration property.incremental
An optional
type
component of thedata
field of a signal that specifies the kind of snapshot operation to run.
Currently, the only valid option is the default value,incremental
.
Specifying atype
value in the SQL query that you submit to the signaling table is optional.
If you do not specify a value, the connector runs an incremental snapshot.
The following example, shows the JSON for an incremental snapshot event that is captured by a connector.
Example: Incremental snapshot event message
{ "before":null, "after": { "pk":"1", "value":"New data" }, "source": { ... "snapshot":"incremental" 1 }, "op":"r", 2 "ts_ms":"1620393591654", "transaction":null }
Item | Field name | Description |
---|---|---|
1 |
|
Specifies the type of snapshot operation to run. |
2 |
|
Specifies the event type. |
The Debezium connector for Db2 does not support schema changes while an incremental snapshot is running.
3.2.2. How Debezium Db2 connectors read change-data tables
After a complete snapshot, when a Debezium Db2 connector starts for the first time, the connector identifies the change-data table for each source table that is in capture mode. The connector does the following for each change-data table:
- Reads change events that were created between the last stored, highest LSN and the current, highest LSN.
- Orders the change events according to the commit LSN and the change LSN for each event. This ensures that the connector emits the change events in the order in which the table changes occurred.
- Passes commit and change LSNs as offsets to Kafka Connect.
- Stores the highest LSN that the connector passed to Kafka Connect.
After a restart, the connector resumes emitting change events from the offset (commit and change LSNs) where it left off. While the connector is running and emitting change events, if you remove a table from capture mode or add a table to capture mode, the connector detects the change, and modifies its behavior accordingly.
3.2.3. Default names of Kafka topics that receive Debezium Db2 change event records
By default, the Db2 connector writes change events for all of the INSERT
, UPDATE
, and DELETE
operations that occur in a table to a single Apache Kafka topic that is specific to that table. The connector uses the following convention to name change event topics:
databaseName.schemaName.tableName
The following list provides definitions for the components of the default name:
- databaseName
-
The logical name of the connector as specified by the
database.server.name
connector configuration property. - schemaName
- The name of the schema in which the operation occurred.
- tableName
- The name of the table in which the operation occurred.
For example, consider a Db2 installation with the mydatabase
database, which contains four tables: PRODUCTS
, PRODUCTS_ON_HAND
, CUSTOMERS
, and ORDERS
that are in the MYSCHEMA
schema. The connector would emit events to these four Kafka topics:
-
mydatabase.MYSCHEMA.PRODUCTS
-
mydatabase.MYSCHEMA.PRODUCTS_ON_HAND
-
mydatabase.MYSCHEMA.CUSTOMERS
-
mydatabase.MYSCHEMA.ORDERS
The connector applies similar naming conventions to label its internal database history topics, schema change topics, and transaction metadata topics.
If the default topic name do not meet your requirements, you can configure custom topic names. To configure custom topic names, you specify regular expressions in the logical topic routing SMT. For more information about using the logical topic routing SMT to customize topic naming, see Topic routing.
3.2.4. About the Debezium Db2 connector schema change topic
You can configure a Debezium Db2 connector to produce schema change events that describe schema changes that are applied to captured tables in the database.
Debezium emits a message to the schema change topic when:
- A new table goes into capture mode.
- A table is removed from capture mode.
- During a database schema update, there is a change in the schema for a table that is in capture mode.
The connector writes schema change events to a Kafka schema change topic that has the name <serverName>
where <serverName>
is the logical server name that is specified in the database.server.name
connector configuration property. Messages that the connector sends to the schema change topic contain a payload that includes the following elements:
databaseName
-
The name of the database to which the statements are applied. The value of
databaseName
serves as the message key. pos
- The position in the binlog where the statements appear.
tableChanges
-
A structured representation of the entire table schema after the schema change. The
tableChanges
field contains an array that includes entries for each column of the table. Because the structured representation presents data in JSON or Avro format, consumers can easily read messages without first processing them through a DDL parser.
For a table that is in capture mode, the connector not only stores the history of schema changes in the schema change topic, but also in an internal database history topic. The internal database history topic is for connector use only and it is not intended for direct use by consuming applications. Ensure that applications that require notifications about schema changes consume that information only from the schema change topic.
Never partition the database history topic. For the database history topic to function correctly, it must maintain a consistent, global order of the event records that the connector emits to it.
To ensure that the topic is not split among partitions, set the partition count for the topic by using one of the following methods:
-
If you create the database history topic manually, specify a partition count of
1
. -
If you use the Apache Kafka broker to create the database history topic automatically, the topic is created, set the value of the Kafka
num.partitions
configuration option to1
.
The format of messages that a connector emits to its schema change topic is in an incubating state and can change without notice.
Example: Message emitted to the Db2 connector schema change topic
The following example shows a message in the schema change topic. The message contains a logical representation of the table schema.
{ "schema": { ... }, "payload": { "source": { "version": "1.7.2.Final", "connector": "db2", "name": "db2", "ts_ms": 1588252618953, "snapshot": "true", "db": "testdb", "schema": "DB2INST1", "table": "CUSTOMERS", "change_lsn": null, "commit_lsn": "00000025:00000d98:00a2", "event_serial_no": null }, "databaseName": "TESTDB", 1 "schemaName": "DB2INST1", "ddl": null, 2 "tableChanges": [ 3 { "type": "CREATE", 4 "id": "\"DB2INST1\".\"CUSTOMERS\"", 5 "table": { 6 "defaultCharsetName": null, "primaryKeyColumnNames": [ 7 "ID" ], "columns": [ 8 { "name": "ID", "jdbcType": 4, "nativeType": null, "typeName": "int identity", "typeExpression": "int identity", "charsetName": null, "length": 10, "scale": 0, "position": 1, "optional": false, "autoIncremented": false, "generated": false }, { "name": "FIRST_NAME", "jdbcType": 12, "nativeType": null, "typeName": "varchar", "typeExpression": "varchar", "charsetName": null, "length": 255, "scale": null, "position": 2, "optional": false, "autoIncremented": false, "generated": false }, { "name": "LAST_NAME", "jdbcType": 12, "nativeType": null, "typeName": "varchar", "typeExpression": "varchar", "charsetName": null, "length": 255, "scale": null, "position": 3, "optional": false, "autoIncremented": false, "generated": false }, { "name": "EMAIL", "jdbcType": 12, "nativeType": null, "typeName": "varchar", "typeExpression": "varchar", "charsetName": null, "length": 255, "scale": null, "position": 4, "optional": false, "autoIncremented": false, "generated": false } ] } } ] } }
Item | Field name | Description |
---|---|---|
1 |
| Identifies the database and the schema that contain the change. |
2 |
|
Always |
3 |
| An array of one or more items that contain the schema changes generated by a DDL command. |
4 |
| Describes the kind of change. The value is one of the following:
|
5 |
| Full identifier of the table that was created, altered, or dropped. |
6 |
| Represents table metadata after the applied change. |
7 |
| List of columns that compose the table’s primary key. |
8 |
| Metadata for each column in the changed table. |
In messages that the connector sends to the schema change topic, the message key is the name of the database that contains the schema change. In the following example, the payload
field contains the key:
{ "schema": { "type": "struct", "fields": [ { "type": "string", "optional": false, "field": "databaseName" } ], "optional": false, "name": "io.debezium.connector.db2.SchemaChangeKey" }, "payload": { "databaseName": "TESTDB" } }
3.2.5. Debezium Db2 connector-generated events that represent transaction boundaries
Debezium can generate events that represent transaction boundaries and that enrich change data event messages.
Debezium registers and receives metadata only for transactions that occur after you deploy the connector. Metadata for transactions that occur before you deploy the connector is not available.
Debezium generates transaction boundary events for the BEGIN
and END
delimiters in every transaction. Transaction boundary events contain the following fields:
status
-
BEGIN
orEND
. id
- String representation of the unique transaction identifier.
event_count
(forEND
events)- Total number of events emitted by the transaction.
data_collections
(forEND
events)-
An array of pairs of
data_collection
andevent_count
elements. that indicates the number of events that the connector emits for changes that originate from a data collection.
Example
{ "status": "BEGIN", "id": "00000025:00000d08:0025", "event_count": null, "data_collections": null } { "status": "END", "id": "00000025:00000d08:0025", "event_count": 2, "data_collections": [ { "data_collection": "testDB.dbo.tablea", "event_count": 1 }, { "data_collection": "testDB.dbo.tableb", "event_count": 1 } ] }
The connector emits transaction events to the <database.server.name>
.transaction
topic.
Data change event enrichment
When transaction metadata is enabled the connector enriches the change event Envelope
with a new transaction
field. This field provides information about every event in the form of a composite of fields:
id
- String representation of unique transaction identifier.
total_order
- The absolute position of the event among all events generated by the transaction.
data_collection_order
- The per-data collection position of the event among all events that were emitted by the transaction.
Following is an example of a message:
{ "before": null, "after": { "pk": "2", "aa": "1" }, "source": { ... }, "op": "c", "ts_ms": "1580390884335", "transaction": { "id": "00000025:00000d08:0025", "total_order": "1", "data_collection_order": "1" } }
3.3. Descriptions of Debezium Db2 connector data change events
The Debezium Db2 connector generates a data change event for each row-level INSERT
, UPDATE
, and DELETE
operation. Each event contains a key and a value. The structure of the key and the value depends on the table that was changed.
Debezium and Kafka Connect are designed around continuous streams of event messages. However, the structure of these events may change over time, which can be difficult for consumers to handle. To address this, each event contains the schema for its content or, if you are using a schema registry, a schema ID that a consumer can use to obtain the schema from the registry. This makes each event self-contained.
The following skeleton JSON shows the basic four parts of a change event. However, how you configure the Kafka Connect converter that you choose to use in your application determines the representation of these four parts in change events. A schema
field is in a change event only when you configure the converter to produce it. Likewise, the event key and event payload are in a change event only if you configure a converter to produce it. If you use the JSON converter and you configure it to produce all four basic change event parts, change events have this structure:
{ "schema": { 1 ... }, "payload": { 2 ... }, "schema": { 3 ... }, "payload": { 4 ... }, }
Item | Field name | Description |
---|---|---|
1 |
|
The first |
2 |
|
The first |
3 |
|
The second |
4 |
|
The second |
By default, the connector streams change event records to topics with names that are the same as the event’s originating table. See topic names.
The Debezium Db2 connector ensures that all Kafka Connect schema names adhere to the Avro schema name format. This means that the logical server name must start with a Latin letter or an underscore, that is, a-z, A-Z, or _. Each remaining character in the logical server name and each character in the database and table names must be a Latin letter, a digit, or an underscore, that is, a-z, A-Z, 0-9, or \_. If there is an invalid character it is replaced with an underscore character.
This can lead to unexpected conflicts if the logical server name, a database name, or a table name contains invalid characters, and the only characters that distinguish names from one another are invalid and thus replaced with underscores.
Also, Db2 names for databases, schemas, and tables can be case sensitive. This means that the connector could emit event records for more than one table to the same Kafka topic.
Details are in the following topics:
3.3.1. About keys in Debezium db2 change events
A change event’s key contains the schema for the changed table’s key and the changed row’s actual key. Both the schema and its corresponding payload contain a field for each column in the changed table’s PRIMARY KEY
(or unique constraint) at the time the connector created the event.
Consider the following customers
table, which is followed by an example of a change event key for this table.
Example table
CREATE TABLE customers ( ID INTEGER IDENTITY(1001,1) NOT NULL PRIMARY KEY, FIRST_NAME VARCHAR(255) NOT NULL, LAST_NAME VARCHAR(255) NOT NULL, EMAIL VARCHAR(255) NOT NULL UNIQUE );
Example change event key
Every change event that captures a change to the customers
table has the same event key schema. For as long as the customers
table has the previous definition, every change event that captures a change to the customers
table has the following key structure. In JSON, it looks like this:
{ "schema": { 1 "type": "struct", "fields": [ 2 { "type": "int32", "optional": false, "field": "ID" } ], "optional": false, 3 "name": "mydatabase.MYSCHEMA.CUSTOMERS.Key" 4 }, "payload": { 5 "ID": 1004 } }
Item | Field name | Description |
---|---|---|
1 |
|
The schema portion of the key specifies a Kafka Connect schema that describes what is in the key’s |
2 |
|
Specifies each field that is expected in the |
3 |
|
Indicates whether the event key must contain a value in its |
4 |
|
Name of the schema that defines the structure of the key’s payload. This schema describes the structure of the primary key for the table that was changed. Key schema names have the format connector-name.database-name.table-name.
|
5 |
|
Contains the key for the row for which this change event was generated. In this example, the key, contains a single |
3.3.2. About values in Debezium Db2 change events
The value in a change event is a bit more complicated than the key. Like the key, the value has a schema
section and a payload
section. The schema
section contains the schema that describes the Envelope
structure of the payload
section, including its nested fields. Change events for operations that create, update or delete data all have a value payload with an envelope structure.
Consider the same sample table that was used to show an example of a change event key:
Example table
CREATE TABLE customers ( ID INTEGER IDENTITY(1001,1) NOT NULL PRIMARY KEY, FIRST_NAME VARCHAR(255) NOT NULL, LAST_NAME VARCHAR(255) NOT NULL, EMAIL VARCHAR(255) NOT NULL UNIQUE );
The event value portion of every change event for the customers
table specifies the same schema. The event value’s payload varies according to the event type:
create events
The following example shows the value portion of a change event that the connector generates for an operation that creates data in the customers
table:
{ "schema": { 1 "type": "struct", "fields": [ { "type": "struct", "fields": [ { "type": "int32", "optional": false, "field": "ID" }, { "type": "string", "optional": false, "field": "FIRST_NAME" }, { "type": "string", "optional": false, "field": "LAST_NAME" }, { "type": "string", "optional": false, "field": "EMAIL" } ], "optional": true, "name": "mydatabase.MYSCHEMA.CUSTOMERS.Value", 2 "field": "before" }, { "type": "struct", "fields": [ { "type": "int32", "optional": false, "field": "ID" }, { "type": "string", "optional": false, "field": "FIRST_NAME" }, { "type": "string", "optional": false, "field": "LAST_NAME" }, { "type": "string", "optional": false, "field": "EMAIL" } ], "optional": true, "name": "mydatabase.MYSCHEMA.CUSTOMERS.Value", "field": "after" }, { "type": "struct", "fields": [ { "type": "string", "optional": false, "field": "version" }, { "type": "string", "optional": false, "field": "connector" }, { "type": "string", "optional": false, "field": "name" }, { "type": "int64", "optional": false, "field": "ts_ms" }, { "type": "boolean", "optional": true, "default": false, "field": "snapshot" }, { "type": "string", "optional": false, "field": "db" }, { "type": "string", "optional": false, "field": "schema" }, { "type": "string", "optional": false, "field": "table" }, { "type": "string", "optional": true, "field": "change_lsn" }, { "type": "string", "optional": true, "field": "commit_lsn" }, ], "optional": false, "name": "io.debezium.connector.db2.Source", 3 "field": "source" }, { "type": "string", "optional": false, "field": "op" }, { "type": "int64", "optional": true, "field": "ts_ms" } ], "optional": false, "name": "mydatabase.MYSCHEMA.CUSTOMERS.Envelope" 4 }, "payload": { 5 "before": null, 6 "after": { 7 "ID": 1005, "FIRST_NAME": "john", "LAST_NAME": "doe", "EMAIL": "john.doe@example.org" }, "source": { 8 "version": "1.7.2.Final", "connector": "db2", "name": "myconnector", "ts_ms": 1559729468470, "snapshot": false, "db": "mydatabase", "schema": "MYSCHEMA", "table": "CUSTOMERS", "change_lsn": "00000027:00000758:0003", "commit_lsn": "00000027:00000758:0005", }, "op": "c", 9 "ts_ms": 1559729471739 10 } }
Item | Field name | Description |
---|---|---|
1 |
| The value’s schema, which describes the structure of the value’s payload. A change event’s value schema is the same in every change event that the connector generates for a particular table. |
2 |
|
In the |
3 |
|
|
4 |
|
|
5 |
|
The value’s actual data. This is the information that the change event is providing. |
6 |
|
An optional field that specifies the state of the row before the event occurred. When the |
7 |
|
An optional field that specifies the state of the row after the event occurred. In this example, the |
8 |
|
Mandatory field that describes the source metadata for the event. The
|
9 |
|
Mandatory string that describes the type of operation that caused the connector to generate the event. In this example,
|
10 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
update events
The value of a change event for an update in the sample customers
table has the same schema as a create event for that table. Likewise, the update event value’s payload has the same structure. However, the event value payload contains different values in an update event. Here is an example of a change event value in an event that the connector generates for an update in the customers
table:
{ "schema": { ... }, "payload": { "before": { 1 "ID": 1005, "FIRST_NAME": "john", "LAST_NAME": "doe", "EMAIL": "john.doe@example.org" }, "after": { 2 "ID": 1005, "FIRST_NAME": "john", "LAST_NAME": "doe", "EMAIL": "noreply@example.org" }, "source": { 3 "version": "1.7.2.Final", "connector": "db2", "name": "myconnector", "ts_ms": 1559729995937, "snapshot": false, "db": "mydatabase", "schema": "MYSCHEMA", "table": "CUSTOMERS", "change_lsn": "00000027:00000ac0:0002", "commit_lsn": "00000027:00000ac0:0007", }, "op": "u", 4 "ts_ms": 1559729998706 5 } }
Item | Field name | Description |
---|---|---|
1 |
|
An optional field that specifies the state of the row before the event occurred. In an update event value, the |
2 |
|
An optional field that specifies the state of the row after the event occurred. You can compare the |
3 |
|
Mandatory field that describes the source metadata for the event. The
|
4 |
|
Mandatory string that describes the type of operation. In an update event value, the |
5 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
Updating the columns for a row’s primary/unique key changes the value of the row’s key. When a key changes, Debezium outputs three events: a DELETE
event and a tombstone event with the old key for the row, followed by an event with the new key for the row.
delete events
The value in a delete change event has the same schema
portion as create and update events for the same table. The event value payload
in a delete event for the sample customers
table looks like this:
{ "schema": { ... }, }, "payload": { "before": { 1 "ID": 1005, "FIRST_NAME": "john", "LAST_NAME": "doe", "EMAIL": "noreply@example.org" }, "after": null, 2 "source": { 3 "version": "1.7.2.Final", "connector": "db2", "name": "myconnector", "ts_ms": 1559730445243, "snapshot": false, "db": "mydatabase", "schema": "MYSCHEMA", "table": "CUSTOMERS", "change_lsn": "00000027:00000db0:0005", "commit_lsn": "00000027:00000db0:0007" }, "op": "d", 4 "ts_ms": 1559730450205 5 } }
Item | Field name | Description |
---|---|---|
1 |
|
Optional field that specifies the state of the row before the event occurred. In a delete event value, the |
2 |
|
Optional field that specifies the state of the row after the event occurred. In a delete event value, the |
3 |
|
Mandatory field that describes the source metadata for the event. In a delete event value, the
|
4 |
|
Mandatory string that describes the type of operation. The |
5 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
A delete change event record provides a consumer with the information it needs to process the removal of this row. The old values are included because some consumers might require them in order to properly handle the removal.
Db2 connector events are designed to work with Kafka log compaction. Log compaction enables removal of some older messages as long as at least the most recent message for every key is kept. This lets Kafka reclaim storage space while ensuring that the topic contains a complete data set and can be used for reloading key-based state.
When a row is deleted, the delete event value still works with log compaction, because Kafka can remove all earlier messages that have that same key. However, for Kafka to remove all messages that have that same key, the message value must be null
. To make this possible, after Debezium’s Db2 connector emits a delete event, the connector emits a special tombstone event that has the same key but a null
value.
3.4. How Debezium Db2 connectors map data types
Db2’s data types are described in Db2 SQL Data Types.
The Db2 connector represents changes to rows with events that are structured like the table in which the row exists. The event contains a field for each column value. How that value is represented in the event depends on the Db2 data type of the column. This section describes these mappings.
Details are in the following sections:
Basic types
The following table describes how the connector maps each of the Db2 data types to a literal type and a semantic type in event fields.
-
literal type describes how the value is represented using Kafka Connect schema types:
INT8
,INT16
,INT32
,INT64
,FLOAT32
,FLOAT64
,BOOLEAN
,STRING
,BYTES
,ARRAY
,MAP
, andSTRUCT
. - semantic type describes how the Kafka Connect schema captures the meaning of the field using the name of the Kafka Connect schema for the field.
Db2 data type | Literal type (schema type) | Semantic type (schema name) and Notes |
---|---|---|
|
| Only snapshots can be taken from tables with BOOLEAN type columns. Currently SQL Replication on Db2 does not support BOOLEAN, so Debezium can not perform CDC on those tables. Consider using a different type. |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
|
|
|
|
|
|
|
|
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
|
|
|
|
|
|
| n/a |
|
| n/a |
|
| n/a |
|
|
|
If present, a column’s default value is propagated to the corresponding field’s Kafka Connect schema. Change events contain the field’s default value unless an explicit column value had been given. Consequently, there is rarely a need to obtain the default value from the schema.
Temporal types
Other than Db2’s DATETIMEOFFSET
data type, which contains time zone information, how temporal types are mapped depends on the value of the time.precision.mode
connector configuration property. The following sections describe these mappings:
time.precision.mode=adaptive
When the time.precision.mode
configuration property is set to adaptive
, the default, the connector determines the literal type and semantic type based on the column’s data type definition. This ensures that events exactly represent the values in the database.
Db2 data type | Literal type (schema type) | Semantic type (schema name) and Notes |
---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
time.precision.mode=connect
When the time.precision.mode
configuration property is set to connect
, the connector uses Kafka Connect logical types. This may be useful when consumers can handle only the built-in Kafka Connect logical types and are unable to handle variable-precision time values. However, since Db2 supports tenth of a microsecond precision, the events generated by a connector with the connect
time precision results in a loss of precision when the database column has a fractional second precision value that is greater than 3.
Db2 data type | Literal type (schema type) | Semantic type (schema name) and Notes |
---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Timestamp types
The DATETIME
, SMALLDATETIME
and DATETIME2
types represent a timestamp without time zone information. Such columns are converted into an equivalent Kafka Connect value based on UTC. For example, the DATETIME2
value "2018-06-20 15:13:16.945104" is represented by an io.debezium.time.MicroTimestamp
with the value "1529507596945104".
The timezone of the JVM running Kafka Connect and Debezium does not affect this conversion.
Db2 data type | Literal type (schema type) | Semantic type (schema name) and Notes |
---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
3.5. Setting up Db2 to run a Debezium connector
For Debezium to capture change events that are committed to Db2 tables, a Db2 database administrator with the necessary privileges must configure tables in the database for change data capture. After you begin to run Debezium you can adjust the configuration of the capture agent to optimize performance.
For details about setting up Db2 for use with the Debezium connector, see the following sections:
3.5.1. Configuring Db2 tables for change data capture
To put tables into capture mode, Debezium provides a set of user-defined functions (UDFs) for your convenience. The procedure here shows how to install and run these management UDFs. Alternatively, you can run Db2 control commands to put tables into capture mode. The administrator must then enable CDC for each table that you want Debezium to capture.
Prerequisites
-
You are logged in to Db2 as the
db2instl
user. - On the Db2 host, the Debezium management UDFs are available in the $HOME/asncdctools/src directory. UDFs are available from the Debezium examples repository.
Procedure
Compile the Debezium management UDFs on the Db2 server host by using the
bldrtn
command provided with Db2:cd $HOME/asncdctools/src
./bldrtn asncdc
Start the database if it is not already running. Replace
DB_NAME
with the name of the database that you want Debezium to connect to.db2 start db DB_NAME
Ensure that JDBC can read the Db2 metadata catalog:
cd $HOME/sqllib/bnd
db2 bind db2schema.bnd blocking all grant public sqlerror continue
Ensure that the database was recently backed-up. The ASN agents must have a recent starting point to read from. If you need to perform a backup, run the following commands, which prune the data so that only the most recent version is available. If you do not need to retain the older versions of the data, specify
dev/null
for the backup location.Back up the database. Replace
DB_NAME
andBACK_UP_LOCATION
with appropriate values:db2 backup db DB_NAME to BACK_UP_LOCATION
Restart the database:
db2 restart db DB_NAME
Connect to the database to install the Debezium management UDFs. It is assumed that you are logged in as the
db2instl
user so the UDFs should be installed on thedb2inst1
user.db2 connect to DB_NAME
Copy the Debezium management UDFs and set permissions for them:
cp $HOME/asncdctools/src/asncdc $HOME/sqllib/function
chmod 777 $HOME/sqllib/function
Enable the Debezium UDF that starts and stops the ASN capture agent:
db2 -tvmf $HOME/asncdctools/src/asncdc_UDF.sql
Create the ASN control tables:
$ db2 -tvmf $HOME/asncdctools/src/asncdctables.sql
Enable the Debezium UDF that adds tables to capture mode and removes tables from capture mode:
$ db2 -tvmf $HOME/asncdctools/src/asncdcaddremove.sql
After you set up the Db2 server, use the UDFs to control Db2 replication (ASN) with SQL commands. Some of the UDFs expect a return value in which case you use the SQL
VALUE
statement to invoke them. For other UDFs, use the SQLCALL
statement.Start the ASN agent:
VALUES ASNCDC.ASNCDCSERVICES('start','asncdc');
The preceding statement returns one of the following results:
-
asncap is already running
start -->
<COMMAND>
In this case, enter the specified
<COMMAND>
in the terminal window as shown in the following example:/database/config/db2inst1/sqllib/bin/asncap capture_schema=asncdc capture_server=SAMPLE &
-
Put tables into capture mode. Invoke the following statement for each table that you want to put into capture. Replace
MYSCHEMA
with the name of the schema that contains the table you want to put into capture mode. Likewise, replaceMYTABLE
with the name of the table to put into capture mode:CALL ASNCDC.ADDTABLE('MYSCHEMA', 'MYTABLE');
Reinitialize the ASN service:
VALUES ASNCDC.ASNCDCSERVICES('reinit','asncdc');
Additional resources
3.5.2. Effect of Db2 capture agent configuration on server load and latency
When a database administrator enables change data capture for a source table, the capture agent begins to run. The agent reads new change event records from the transaction log and replicates the event records to a capture table. Between the time that a change is committed in the source table, and the time that the change appears in the corresponding change table, there is always a small latency interval. This latency interval represents a gap between when changes occur in the source table and when they become available for Debezium to stream to Apache Kafka.
Ideally, for applications that must respond quickly to changes in data, you want to maintain close synchronization between the source and capture tables. You might imagine that running the capture agent to continuously process change events as rapidly as possible might result in increased throughput and reduced latency — populating change tables with new event records as soon as possible after the events occur, in near real time. However, this is not necessarily the case. There is a performance penalty to pay in the pursuit of more immediate synchronization. Each time that the change agent queries the database for new event records, it increases the CPU load on the database host. The additional load on the server can have a negative effect on overall database performance, and potentially reduce transaction efficiency, especially during times of peak database use.
It’s important to monitor database metrics so that you know if the database reaches the point where the server can no longer support the capture agent’s level of activity. If you experience performance issues while running the capture agent, adjust capture agent settings to reduce CPU load.
3.5.3. Db2 capture agent configuration parameters
On Db2, the IBMSNAP_CAPPARMS
table contains parameters that control the behavior of the capture agent. You can adjust the values for these parameters to balance the configuration of the capture process to reduce CPU load and still maintain acceptable levels of latency.
Specific guidance about how to configure Db2 capture agent parameters is beyond the scope of this documentation.
In the IBMSNAP_CAPPARMS
table, the following parameters have the greatest effect on reducing CPU load:
COMMIT_INTERVAL
- Specifies the number of seconds that the capture agent waits to commit data to the change data tables.
- A higher value reduces the load on the database host and increases latency.
-
The default value is
30
.
SLEEP_INTERVAL
- Specifies the number of seconds that the capture agent waits to start a new commit cycle after it reaches the end of the active transaction log.
- A higher value reduces the load on the server, and increases latency.
-
The default value is
5
.
Additional resources
- For more information about capture agent parameters, see the Db2 documentation.
3.6. Deployment of Debezium Db2 connectors
You can use either of the following methods to deploy a Debezium Db2 connector:
The Debezium Db2 connector requires the Db2 JDBC driver to connect to Db2 databases. For information about how to obtain the driver, see Obtaining the Db2 JDBC driver.
Additional resources
3.6.1. Obtaining the Db2 JDBC driver
Due to licensing requirements, the Db2 JDBC driver file is not included in the Debezium Db2 connector archive. Regardless of the deployment method that you use, you must download the driver file to complete the deployment.
The following steps describe how to obtain the driver and use it your your environment.
Procedure
From a browser, navigate to the IBM Support site and download the JDBC driver that matches your version of Db2.
-
If you use a Dockerfile to build the connector, copy the downloaded file to the directory that contains the Debezium Db2 connector files, for example,
<kafka_home>/libs
directory. If you use AMQ Streams to add the connector to your Kafka Connect image:
- Deploy the driver to a Maven repository or to another HTTP server that is available to your OpenShift cluster.
-
Add the artifact URL to the
KafkaConnect
custom resource.
-
If you use a Dockerfile to build the connector, copy the downloaded file to the directory that contains the Debezium Db2 connector files, for example,
After you apply the KafkaConnector
resource to deploy the connector, the connector is configured to use the specified driver.
3.6.2. Db2 connector deployment using AMQ Streams
Beginning with Debezium 1.7, the preferred method for deploying a Debezium connector is to use AMQ Streams to build a Kafka Connect container image that includes the connector plug-in.
During the deployment process, you create and use the following custom resources (CRs):
-
A
KafkaConnect
CR that defines your Kafka Connect instance and includes information about the connector artifacts needs to include in the image. -
A
KafkaConnector
CR that provides details that include information the connector uses to access the source database. After AMQ Streams starts the Kafka Connect pod, you start the connector by applying theKafkaConnector
CR.
In the build specification for the Kafka Connect image, you can specify the connectors that are available to deploy. For each connector plug-in, you can also specify other components that you want to make available for deployment. For example, you can add Service Registry artifacts, or the Debezium scripting component. When AMQ Streams builds the Kafka Connect image, it downloads the specified artifacts, and incorporates them into the image.
The spec.build.output
parameter in the KafkaConnect
CR specifies where to store the resulting Kafka Connect container image. Container images can be stored in a Docker registry, or in an OpenShift ImageStream. To store images in an ImageStream, you must create the ImageStream before you deploy Kafka Connect. ImageStreams are not created automatically.
If you use a KafkaConnect
resource to create a cluster, afterwards you cannot use the Kafka Connect REST API to create or update connectors. You can still use the REST API to retrieve information.
Additional resources
- Configuring Kafka Connect in Using AMQ Streams on OpenShift.
- Creating a new container image automatically using AMQ Streams in Deploying and Upgrading AMQ Streams on OpenShift.
3.6.3. Using AMQ Streams to deploy a Debezium Db2 connector
With earlier versions of AMQ Streams, to deploy Debezium connectors on OpenShift, it was necessary to first build a Kafka Connect image for the connector. The current preferred method for deploying connectors on OpenShift is to use a build configuration in AMQ Streams to automatically build a Kafka Connect container image that includes the Debezium connector plug-ins that you want to use.
During the build process, the AMQ Streams Operator transforms input parameters in a KafkaConnect
custom resource, including Debezium connector definitions, into a Kafka Connect container image. The build downloads the necessary artifacts from the Red Hat Maven repository or another configured HTTP server. The newly created container is pushed to the container registry that is specified in .spec.build.output
, and is used to deploy a Kafka Connect pod. After AMQ Streams builds the Kafka Connect image, you create KafkaConnector
custom resources to start the connectors that are included in the build.
Prerequisites
- You have access to an OpenShift cluster on which the cluster Operator is installed.
- The AMQ Streams Operator is running.
- An Apache Kafka cluster is deployed as documented in Deploying and Upgrading AMQ Streams on OpenShift.
- You have a Red Hat Integration license.
- Kafka Connect is deployed on AMQ Streams.
-
The OpenShift
oc
CLI client is installed or you have access to the OpenShift Container Platform web console. Depending on how you intend to store the Kafka Connect build image, you need registry permissions or you must create an ImageStream resource:
- To store the build image in an image registry, such as Red Hat Quay.io or Docker Hub
- An account and permissions to create and manage images in the registry.
- To store the build image as a native OpenShift ImageStream
- An ImageStream resource is deployed to the cluster. You must explicitly create an ImageStream for the cluster. ImageStreams are not available by default.
Procedure
- Log in to the OpenShift cluster.
Create a Debezium
KafkaConnect
custom resource (CR) for the connector, or modify an existing one. For example, create aKafkaConnect
CR that specifies themetadata.annotations
andspec.build
properties, as shown in the following example. Save the file with a name such asdbz-connect.yaml
.Example 3.1. A
dbz-connect.yaml
file that defines aKafkaConnect
custom resource that includes a Debezium connectorapiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnect metadata: name: debezium-kafka-connect-cluster annotations: strimzi.io/use-connector-resources: "true" 1 spec: version: 3.00 build: 2 output: 3 type: imagestream 4 image: debezium-streams-connect:latest plugins: 5 - name: debezium-connector-db2 artifacts: - type: zip 6 url: https://maven.repository.redhat.com/ga/io/debezium/debezium-connector-db2/1.7.2.Final-redhat-<build_number>/debezium-connector-db2-1.7.2.Final-redhat-<build_number>-plugin.zip 7 - type: zip url: https://maven.repository.redhat.com/ga/io/apicurio/apicurio-registry-distro-connect-converter/2.0-redhat-<build-number>/apicurio-registry-distro-connect-converter-2.0-redhat-<build-number>.zip - type: zip url: https://maven.repository.redhat.com/ga/io/debezium/debezium-scripting/1.7.2.Final/debezium-scripting-1.7.2.Final.zip bootstrapServers: debezium-kafka-cluster-kafka-bootstrap:9093
Table 3.13. Descriptions of Kafka Connect configuration settings Item Description 1
Sets the
strimzi.io/use-connector-resources
annotation to"true"
to enable the Cluster Operator to useKafkaConnector
resources to configure connectors in this Kafka Connect cluster.2
The
spec.build
configuration specifies where to store the build image and lists the plug-ins to include in the image, along with the location of the plug-in artifacts.3
The
build.output
specifies the registry in which the newly built image is stored.4
Specifies the name and image name for the image output. Valid values for
output.type
aredocker
to push into a container registry like Docker Hub or Quay, orimagestream
to push the image to an internal OpenShift ImageStream. To use an ImageStream, an ImageStream resource must be deployed to the cluster. For more information about specifying thebuild.output
in the KafkaConnect configuration, see the AMQ Streams Build schema reference documentation.5
The
plugins
configuration lists all of the connectors that you want to include in the Kafka Connect image. For each entry in the list, specify a plug-inname
, and information for about the artifacts that are required to build the connector. Optionally, for each connector plug-in, you can include other components that you want to be available for use with the connector. For example, you can add Service Registry artifacts, or the Debezium scripting component.6
The value of
artifacts.type
specifies the file type of the artifact specified in theartifacts.url
. Valid types arezip
,tgz
, orjar
. Debezium connector archives are provided in.zip
file format. JDBC driver files are in.jar
format. Thetype
value must match the type of the file that is referenced in theurl
field.7
The value of
artifacts.url
specifies the address of an HTTP server, such as a Maven repository, that stores the file for the connector artifact. The OpenShift cluster must have access to the specified server.Apply the
KafkaConnect
build specification to the OpenShift cluster by entering the following command:oc create -f dbz-connect.yaml
Based on the configuration specified in the custom resource, the Streams Operator prepares a Kafka Connect image to deploy.
After the build completes, the Operator pushes the image to the specified registry or ImageStream, and starts the Kafka Connect cluster. The connector artifacts that you listed in the configuration are available in the cluster.Create a
KafkaConnector
resource to define an instance of each connector that you want to deploy.
For example, create the followingKafkaConnector
CR, and save it asdb2-inventory-connector.yaml
Example 3.2. A
db2-inventory-connector.yaml
file that defines theKafkaConnector
custom resource for a Debezium connectorapiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnector metadata: labels: strimzi.io/cluster: debezium-kafka-connect-cluster name: inventory-connector-db2 1 spec: class: io.debezium.connector.db2.Db2ConnectorConnector 2 tasksMax: 1 3 config: 4 database.history.kafka.bootstrap.servers: 'debezium-kafka-cluster-kafka-bootstrap.debezium.svc.cluster.local:9092' database.history.kafka.topic: schema-changes.inventory database.hostname: db2.debezium-db2.svc.cluster.local 5 database.port: 3306 6 database.user: debezium 7 database.password: dbz 8 database.dbname: mydatabase 9 database.server.name: inventory_connector_db2 10 database.include.list: public.inventory 11
Table 3.14. Descriptions of connector configuration settings Item Description 1
The name of the connector to register with the Kafka Connect cluster.
2
The name of the connector class.
3
The number of tasks that can operate concurrently.
4
The connector’s configuration.
5
The address of the host database instance.
6
The port number of the database instance.
7
The name of the user account through which Debezium connects to the database.
8
The password for the database user account.
9
The name of the database to capture changes from.
10
The logical name of the database instance or cluster.
The specified name must be formed only from alphanumeric characters or underscores.
Because the logical name is used as the prefix for any Kafka topics that receive change events from this connector, the name must be unique among the connectors in the cluster.
The namespace is also used in the names of related Kafka Connect schemas, and the namespaces of a corresponding Avro schema if you integrate the connector with the Avro connector.11
The list of tables from which the connector captures change events.
Create the connector resource by running the following command:
oc create -n <namespace> -f <kafkaConnector>.yaml
For example,
oc create -n debezium -f {context}-inventory-connector.yaml
The connector is registered to the Kafka Connect cluster and starts to run against the database that is specified by
spec.config.database.dbname
in theKafkaConnector
CR. After the connector pod is ready, Debezium is running.
You are now ready to verify the Debezium Db2 deployment.
3.6.4. Deploying a Debezium Db2 connector by building a custom Kafka Connect container image from a Dockerfile
To deploy a Debezium Db2 connector, you must build a custom Kafka Connect container image that contains the Debezium connector archive, and then push this container image to a container registry. You then need to create the following custom resources (CRs):
-
A
KafkaConnect
CR that defines your Kafka Connect instance. Theimage
property in the CR specifies the name of the container image that you create to run your Debezium connector. You apply this CR to the OpenShift instance where Red Hat AMQ Streams is deployed. AMQ Streams offers operators and images that bring Apache Kafka to OpenShift. -
A
KafkaConnector
CR that defines your Debezium Db2 connector. Apply this CR to the same OpenShift instance where you applied theKafkaConnect
CR.
Prerequisites
- Db2 is running and you completed the steps to set up Db2 to work with a Debezium connector.
- AMQ Streams is deployed on OpenShift and is running Apache Kafka and Kafka Connect. For more information, see Deploying and Upgrading AMQ Streams on OpenShift.
- Podman or Docker is installed.
- You obtained the required JDBC driver for Db2.
-
You have an account and permissions to create and manage containers in the container registry (such as
quay.io
ordocker.io
) to which you plan to add the container that will run your Debezium connector.
Procedure
Create the Debezium Db2 container for Kafka Connect:
- Download the Debezium Db2 connector archive.
Extract the Debezium Db2 connector archive to create a directory structure for the connector plug-in, for example:
./my-plugins/ ├── debezium-connector-db2 │ ├── ...
Create a Dockerfile that uses
registry.redhat.io/amq7/amq-streams-kafka-30-rhel8:2.0.0
as the base image. For example, from a terminal window, enter the following, replacingmy-plugins
with the name of your plug-ins directory:cat <<EOF >debezium-container-for-db2.yaml 1 FROM registry.redhat.io/amq7/amq-streams-kafka-30-rhel8:2.0.0 USER root:root COPY ./<my-plugins>/ /opt/kafka/plugins/ 2 USER 1001 EOF
The command creates a Dockerfile with the name
debezium-container-for-db2.yaml
in the current directory.Build the container image from the
debezium-container-for-db2.yaml
Docker file that you created in the previous step. From the directory that contains the file, open a terminal window and enter one of the following commands:podman build -t debezium-container-for-db2:latest .
docker build -t debezium-container-for-db2:latest .
The preceding commands build a container image with the name
debezium-container-for-db2
.Push your custom image to a container registry, such as quay.io or an internal container registry. The container registry must be available to the OpenShift instance where you want to deploy the image. Enter one of the following commands:
podman push <myregistry.io>/debezium-container-for-db2:latest
docker push <myregistry.io>/debezium-container-for-db2:latest
Create a new Debezium Db2
KafkaConnect
custom resource (CR). For example, create aKafkaConnect
CR with the namedbz-connect.yaml
that specifiesannotations
andimage
properties as shown in the following example:apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnect metadata: name: my-connect-cluster annotations: strimzi.io/use-connector-resources: "true" 1 spec: #... image: debezium-container-for-db2 2
- 1
metadata.annotations
indicates to the Cluster Operator thatKafkaConnector
resources are used to configure connectors in this Kafka Connect cluster.- 2
spec.image
specifies the name of the image that you created to run your Debezium connector. This property overrides theSTRIMZI_DEFAULT_KAFKA_CONNECT_IMAGE
variable in the Cluster Operator.
Apply the
KafkaConnect
CR to the OpenShift Kafka Connect environment by entering the following command:oc create -f dbz-connect.yaml
The command adds a Kafka Connect instance that specifies the name of the image that you created to run your Debezium connector.
Create a
KafkaConnector
custom resource that configures your Debezium Db2 connector instance.You configure a Debezium Db2 connector in a
.yaml
file that specifies the configuration properties for the connector. The connector configuration might instruct Debezium to produce events for a subset of the schemas and tables, or it might set properties so that Debezium ignores, masks, or truncates values in specified columns that are sensitive, too large, or not needed.The following example configures a Debezium connector that connects to a Db2 server host,
192.168.99.100
, on port50000
. This host has a database namedmydatabase
, a table with the nameinventory
, andfulfillment
is the server’s logical name.Db2
inventory-connector.yaml
apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnector metadata: name: inventory-connector 1 labels: strimzi.io/cluster: my-connect-cluster annotations: strimzi.io/use-connector-resources: 'true' spec: class: io.debezium.connector.db2.Db2Connector 2 tasksMax: 1 3 config: 4 database.hostname: 192.168.99.100 5 database.port: 50000 6 database.user: db2inst1 7 database.password: Password! 8 database.dbname: mydatabase 9 database.server.name: fullfillment 10 database.include.list: public.inventory 11
Table 3.15. Descriptions of connector configuration settings Item Description 1
The name of the connector when we register it with a Kafka Connect cluster.
2
The name of this Db2 connector class.
3
Only one task should operate at any one time.
4
The connector’s configuration.
5
The database host, which is the address of the Db2 instance.
6
The port number of the Db2 instance.
7
The name of the Db2 user.
8
The password for the Db2 user.
9
The name of the database to capture changes from.
10
The logical name of the Db2 instance/cluster, which forms a namespace and is used in the names of the Kafka topics to which the connector writes, the names of Kafka Connect schemas, and the namespaces of the corresponding Avro schema when the Avro Connector is used.
11
A list of all tables whose changes Debezium should capture.
Create your connector instance with Kafka Connect. For example, if you saved your
KafkaConnector
resource in theinventory-connector.yaml
file, you would run the following command:oc apply -f inventory-connector.yaml
The preceding command registers
inventory-connector
and the connector starts to run against themydatabase
database as defined in theKafkaConnector
CR.
For the complete list of the configuration properties that you can set for the Debezium Db2 connector, see Db2 connector properties.
Results
After the connector starts, it performs a consistent snapshot of the Db2 database tables that the connector is configured to capture changes for. The connector then starts generating data change events for row-level operations and streaming change event records to Kafka topics.
3.6.5. Verifying that the Debezium Db2 connector is running
If the connector starts correctly without errors, it creates a topic for each table that the connector is configured to capture. Downstream applications can subscribe to these topics to retrieve information events that occur in the source database.
To verify that the connector is running, you perform the following operations from the OpenShift Container Platform web console, or through the OpenShift CLI tool (oc):
- Verify the connector status.
- Verify that the connector generates topics.
- Verify that topics are populated with events for read operations ("op":"r") that the connector generates during the initial snapshot of each table.
Prerequisites
- A Debezium connector is deployed to AMQ Streams on OpenShift.
-
The OpenShift
oc
CLI client is installed. - You have access to the OpenShift Container Platform web console.
Procedure
Check the status of the
KafkaConnector
resource by using one of the following methods:From the OpenShift Container Platform web console:
- Navigate to Home → Search.
-
On the Search page, click Resources to open the Select Resource box, and then type
KafkaConnector
. - From the KafkaConnectors list, click the name of the connector that you want to check, for example inventory-connector-db2.
- In the Conditions section, verify that the values in the Type and Status columns are set to Ready and True.
From a terminal window:
Enter the following command:
oc describe KafkaConnector <connector-name> -n <project>
For example,
oc describe KafkaConnector inventory-connector-db2 -n debezium
The command returns status information that is similar to the following output:
Example 3.3.
KafkaConnector
resource statusName: inventory-connector-db2 Namespace: debezium Labels: strimzi.io/cluster=debezium-kafka-connect-cluster Annotations: <none> API Version: kafka.strimzi.io/v1beta2 Kind: KafkaConnector ... Status: Conditions: Last Transition Time: 2021-12-08T17:41:34.897153Z Status: True Type: Ready Connector Status: Connector: State: RUNNING worker_id: 10.131.1.124:8083 Name: inventory-connector-db2 Tasks: Id: 0 State: RUNNING worker_id: 10.131.1.124:8083 Type: source Observed Generation: 1 Tasks Max: 1 Topics: inventory_connector_db2 inventory_connector_db2.inventory.addresses inventory_connector_db2.inventory.customers inventory_connector_db2.inventory.geom inventory_connector_db2.inventory.orders inventory_connector_db2.inventory.products inventory_connector_db2.inventory.products_on_hand Events: <none>
Verify that the connector created Kafka topics:
From the OpenShift Container Platform web console.
- Navigate to Home → Search.
-
On the Search page, click Resources to open the Select Resource box, and then type
KafkaTopic
. - From the KafkaTopics list, click the name of the topic that you want to check, for example, inventory-connector-db2.inventory.orders---ac5e98ac6a5d91e04d8ec0dc9078a1ece439081d.
- In the Conditions section, verify that the values in the Type and Status columns are set to Ready and True.
From a terminal window:
Enter the following command:
oc get kafkatopics
The command returns status information that is similar to the following output:
Example 3.4.
KafkaTopic
resource statusNAME CLUSTER PARTITIONS REPLICATION FACTOR READY connect-cluster-configs debezium-kafka-cluster 1 1 True connect-cluster-offsets debezium-kafka-cluster 25 1 True connect-cluster-status debezium-kafka-cluster 5 1 True consumer-offsets---84e7a678d08f4bd226872e5cdd4eb527fadc1c6a debezium-kafka-cluster 50 1 True inventory-connector-db2---a96f69b23d6118ff415f772679da623fbbb99421 debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.addresses---1b6beaf7b2eb57d177d92be90ca2b210c9a56480 debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.customers---9931e04ec92ecc0924f4406af3fdace7545c483b debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.geom---9f7e136091f071bf49ca59bf99e86c713ee58dd5 debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.orders---ac5e98ac6a5d91e04d8ec0dc9078a1ece439081d debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.products---df0746db116844cee2297fab611c21b56f82dcef debezium-kafka-cluster 1 1 True inventory-connector-db2.inventory.products-on-hand---8649e0f17ffcc9212e266e31a7aeea4585e5c6b5 debezium-kafka-cluster 1 1 True schema-changes.inventory debezium-kafka-cluster 1 1 True strimzi-store-topic---effb8e3e057afce1ecf67c3f5d8e4e3ff177fc55 debezium-kafka-cluster 1 1 True strimzi-topic-operator-kstreams-topic-store-changelog---b75e702040b99be8a9263134de3507fc0cc4017b debezium-kafka-cluster 1 1 True
Check topic content.
- From a terminal window, enter the following command:
oc exec -n <project> -it <kafka-cluster> -- /opt/kafka/bin/kafka-console-consumer.sh \ > --bootstrap-server localhost:9092 \ > --from-beginning \ > --property print.key=true \ > --topic=<topic-name>
For example,
oc exec -n debezium -it debezium-kafka-cluster-kafka-0 -- /opt/kafka/bin/kafka-console-consumer.sh \ > --bootstrap-server localhost:9092 \ > --from-beginning \ > --property print.key=true \ > --topic=inventory_connector_db2.inventory.products_on_hand
The format for specifying the topic name is the same as the
oc describe
command returns in Step 1, for example,inventory_connector_db2.inventory.addresses
.For each event in the topic, the command returns information that is similar to the following output:
Example 3.5. Content of a Debezium change event
{"schema":{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"}],"optional":false,"name":"inventory_connector_db2.inventory.products_on_hand.Key"},"payload":{"product_id":101}} {"schema":{"type":"struct","fields":[{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"},{"type":"int32","optional":false,"field":"quantity"}],"optional":true,"name":"inventory_connector_db2.inventory.products_on_hand.Value","field":"before"},{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"},{"type":"int32","optional":false,"field":"quantity"}],"optional":true,"name":"inventory_connector_db2.inventory.products_on_hand.Value","field":"after"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"version"},{"type":"string","optional":false,"field":"connector"},{"type":"string","optional":false,"field":"name"},{"type":"int64","optional":false,"field":"ts_ms"},{"type":"string","optional":true,"name":"io.debezium.data.Enum","version":1,"parameters":{"allowed":"true,last,false"},"default":"false","field":"snapshot"},{"type":"string","optional":false,"field":"db"},{"type":"string","optional":true,"field":"sequence"},{"type":"string","optional":true,"field":"table"},{"type":"int64","optional":false,"field":"server_id"},{"type":"string","optional":true,"field":"gtid"},{"type":"string","optional":false,"field":"file"},{"type":"int64","optional":false,"field":"pos"},{"type":"int32","optional":false,"field":"row"},{"type":"int64","optional":true,"field":"thread"},{"type":"string","optional":true,"field":"query"}],"optional":false,"name":"io.debezium.connector.db2.Source","field":"source"},{"type":"string","optional":false,"field":"op"},{"type":"int64","optional":true,"field":"ts_ms"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"id"},{"type":"int64","optional":false,"field":"total_order"},{"type":"int64","optional":false,"field":"data_collection_order"}],"optional":true,"field":"transaction"}],"optional":false,"name":"inventory_connector_db2.inventory.products_on_hand.Envelope"},"payload":{"before":null,"after":{"product_id":101,"quantity":3},"source":{"version":"1.7.2.Final-redhat-00001","connector":"db2","name":"inventory_connector_db2","ts_ms":1638985247805,"snapshot":"true","db":"inventory","sequence":null,"table":"products_on_hand","server_id":0,"gtid":null,"file":"db2-bin.000003","pos":156,"row":0,"thread":null,"query":null},"op":"r","ts_ms":1638985247805,"transaction":null}}
In the preceding example, the
payload
value shows that the connector snapshot generated a read ("op" ="r"
) event from the tableinventory.products_on_hand
. The"before"
state of theproduct_id
record isnull
, indicating that no previous value exists for the record. The"after"
state shows aquantity
of3
for the item withproduct_id
101
.
3.6.6. Description of Debezium Db2 connector configuration properties
The Debezium Db2 connector has numerous configuration properties that you can use to achieve the right connector behavior for your application. Many properties have default values. Information about the properties is organized as follows:
- Required configuration properties
- Advanced configuration properties
Database history connector configuration properties that control how Debezium processes events that it reads from the database history topic.
- Pass-through database driver properties that control the behavior of the database driver.
Required Debezium Db2 connector configuration properties
The following configuration properties are required unless a default value is available.
Property | Default | Description |
---|---|---|
No default | Unique name for the connector. Attempting to register again with the same name will fail. This property is required by all Kafka Connect connectors. | |
No default |
The name of the Java class for the connector. Always use a value of | |
| The maximum number of tasks that should be created for this connector. The Db2 connector always uses a single task and therefore does not use this value, so the default is always acceptable. | |
No default | IP address or hostname of the Db2 database server. | |
| Integer port number of the Db2 database server. | |
No default | Name of the Db2 database user for connecting to the Db2 database server. | |
No default | Password to use when connecting to the Db2 database server. | |
No default | The name of the Db2 database from which to stream the changes | |
No default | Logical name that identifies and provides a namespace for the particular Db2 database server that hosts the database for which Debezium is capturing changes. Only alphanumeric characters, hyphens, dots and underscores must be used in the database server logical name. The logical name should be unique across all other connectors, since it is used as a topic name prefix for all Kafka topics that receive records from this connector. | |
No default |
An optional, comma-separated list of regular expressions that match fully-qualified table identifiers for tables whose changes you want the connector to capture. Any table not included in the include list does not have its changes captured. Each identifier is of the form schemaName.tableName. By default, the connector captures changes in every non-system table. Do not also set the | |
No default |
An optional, comma-separated list of regular expressions that match fully-qualified table identifiers for tables whose changes you do not want the connector to capture. The connector captures changes in each non-system table that is not included in the exclude list. Each identifier is of the form schemaName.tableName. Do not also set the | |
empty string | An optional, comma-separated list of regular expressions that match the fully-qualified names of columns to exclude from change event values. Fully-qualified names for columns are of the form schemaName.tableName.columnName. Primary key columns are always included in the event’s key, even if they are excluded from the value. | |
n/a |
An optional, comma-separated list of regular expressions that match the fully-qualified names of character-based columns. Fully-qualified names for columns are of the form schemaName.tableName.columnName. In the resulting change event record, the values for the specified columns are replaced with pseudonyms.
A pseudonym consists of the hashed value that results from applying the specified hashAlgorithm and salt. Based on the hash function that is used, referential integrity is maintained, while column values are replaced with pseudonyms. Supported hash functions are described in the MessageDigest section of the Java Cryptography Architecture Standard Algorithm Name Documentation. column.mask.hash.SHA-256.with.salt.CzQMA0cB5K = inventory.orders.customerName, inventory.shipment.customerName
If necessary, the pseudonym is automatically shortened to the length of the column. The connector configuration can include multiple properties that specify different hash algorithms and salts. | |
|
Time, date, and timestamps can be represented with different kinds of precision: | |
|
Controls whether a delete event is followed by a tombstone event. | |
| Boolean value that specifies whether the connector should publish changes in the database schema to a Kafka topic with the same name as the database server ID. Each schema change is recorded with a key that contains the database name and a value that is a JSON structure that describes the schema update. This is independent of how the connector internally records database history. | |
n/a |
An optional, comma-separated list of regular expressions that match the fully-qualified names of character-based columns. Fully-qualified names for columns are of the form schemaName.tableName.columnName. In change event records, values in these columns are truncated if they are longer than the number of characters specified by length in the property name. You can specify multiple properties with different lengths in a single configuration. Length must be a positive integer, for example, | |
n/a |
An optional, comma-separated list of regular expressions that match the fully-qualified names of character-based columns. Fully-qualified names for columns are of the form schemaName.tableName.columnName. In change event values, the values in the specified table columns are replaced with length number of asterisk ( | |
n/a |
An optional, comma-separated list of regular expressions that match the fully-qualified names of columns. Fully-qualified names for columns are of the form databaseName.tableName.columnName, or databaseName.schemaName.tableName.columnName. | |
n/a |
An optional, comma-separated list of regular expressions that match the database-specific data type name for some columns. Fully-qualified data type names are of the form databaseName.tableName.typeName, or databaseName.schemaName.tableName.typeName. | |
empty string | A list of expressions that specify the columns that the connector uses to form custom message keys for change event records that it publishes to the Kafka topics for specified tables.
By default, Debezium uses the primary key column of a table as the message key for records that it emits. In place of the default, or to specify a key for tables that lack a primary key, you can configure custom message keys based on one or more columns.
The property can list entries for multiple tables. Use a semicolon to separate entries for different tables in the list. |
Advanced connector configuration properties
The following advanced configuration properties have defaults that work in most situations and therefore rarely need to be specified in the connector’s configuration.
Property | Default | Description |
---|---|---|
|
Specifies the criteria for performing a snapshot when the connector starts: | |
|
During a snapshot, controls the transaction isolation level and how long the connector locks the tables that are in capture mode. The possible values are: | |
|
Specifies how the connector handles exceptions during processing of events. The possible values are: | |
| Positive integer value that specifies the number of milliseconds the connector should wait for new change events to appear before it starts processing a batch of events. Defaults to 1000 milliseconds, or 1 second. | |
|
Positive integer value for the maximum size of the blocking queue. The connector places change events that it reads from the database log into the blocking queue before writing them to Kafka. This queue can provide backpressure for reading change-data tables when, for example, writing records to Kafka is slower than it should be or Kafka is not available. Events that appear in the queue are not included in the offsets that are periodically recorded by the connector. The | |
| Positive integer value that specifies the maximum size of each batch of events that the connector processes. | |
| Long value for the maximum size in bytes of the blocking queue. The feature is disabled by default, it will be active if it’s set with a positive long value. | |
|
Controls how frequently the connector sends heartbeat messages to a Kafka topic. The default behavior is that the connector does not send heartbeat messages. | |
|
Specifies the prefix for the name of the topic to which the connector sends heartbeat messages. The format for this topic name is | |
No default | An interval in milliseconds that the connector should wait before performing a snapshot when the connector starts. If you are starting multiple connectors in a cluster, this property is useful for avoiding snapshot interruptions, which might cause re-balancing of connectors. | |
| During a snapshot, the connector reads table content in batches of rows. This property specifies the maximum number of rows in a batch. | |
|
Positive integer value that specifies the maximum amount of time (in milliseconds) to wait to obtain table locks when performing a snapshot. If the connector cannot acquire table locks in this interval, the snapshot fails. How the connector performs snapshots provides details. Other possible settings are: | |
No default | Specifies the table rows to include in a snapshot. Use the property if you want a snapshot to include only a subset of the rows in a table. This property affects snapshots only. It does not apply to events that the connector reads from the log.
The property contains a comma-separated list of fully-qualified table names in the form
From a "snapshot.select.statement.overrides": "customer.orders", "snapshot.select.statement.overrides.customer.orders": "SELECT * FROM [customers].[orders] WHERE delete_flag = 0 ORDER BY id DESC"
In the resulting snapshot, the connector includes only the records for which | |
| Indicates whether field names are sanitized to adhere to Avro naming requirements. | |
|
Determines whether the connector generates events with transaction boundaries and enriches change event envelopes with transaction metadata. Specify | |
No default |
comma-separated list of operation types that will be skipped during streaming. The operations include: | |
No default |
Fully-qualified name of the data collection that is used to send signals to the connector. Use the following format to specify the collection name: Signaling is a Technology Preview feature. | |
| The maximum number of rows that the connector fetches and reads into memory during an incremental snapshot chunk. Increasing the chunk size provides greater efficiency, because the snapshot runs fewer snapshot queries of a greater size. However, larger chunk sizes also require more memory to buffer the snapshot data. Adjust the chunk size to a value that provides the best performance in your environment. Incremental snapshots is a Technology Preview feature. |
Debezium connector database history configuration properties
Debezium provides a set of database.history.*
properties that control how the connector interacts with the schema history topic.
The following table describes the database.history
properties for configuring the Debezium connector.
Property | Default | Description |
---|---|---|
The full name of the Kafka topic where the connector stores the database schema history. | ||
A list of host/port pairs that the connector uses for establishing an initial connection to the Kafka cluster. This connection is used for retrieving the database schema history previously stored by the connector, and for writing each DDL statement read from the source database. Each pair should point to the same Kafka cluster used by the Kafka Connect process. | ||
| An integer value that specifies the maximum number of milliseconds the connector should wait during startup/recovery while polling for persisted data. The default is 100ms. | |
|
The maximum number of times that the connector should try to read persisted history data before the connector recovery fails with an error. The maximum amount of time to wait after receiving no data is | |
|
A Boolean value that specifies whether the connector should ignore malformed or unknown database statements or stop processing so a human can fix the issue. The safe default is | |
Deprecated and scheduled for removal in a future release; use |
|
A Boolean value that specifies whether the connector should record all DDL statements
The safe default is |
|
A Boolean value that specifies whether the connector should record all DDL statements
The safe default is |
Pass-through database history properties for configuring producer and consumer clients
Debezium relies on a Kafka producer to write schema changes to database history topics. Similarly, it relies on a Kafka consumer to read from database history topics when a connector starts. You define the configuration for the Kafka producer and consumer clients by assigning values to a set of pass-through configuration properties that begin with the database.history.producer.*
and database.history.consumer.*
prefixes. The pass-through producer and consumer database history properties control a range of behaviors, such as how these clients secure connections with the Kafka broker, as shown in the following example:
database.history.producer.security.protocol=SSL database.history.producer.ssl.keystore.location=/var/private/ssl/kafka.server.keystore.jks database.history.producer.ssl.keystore.password=test1234 database.history.producer.ssl.truststore.location=/var/private/ssl/kafka.server.truststore.jks database.history.producer.ssl.truststore.password=test1234 database.history.producer.ssl.key.password=test1234 database.history.consumer.security.protocol=SSL database.history.consumer.ssl.keystore.location=/var/private/ssl/kafka.server.keystore.jks database.history.consumer.ssl.keystore.password=test1234 database.history.consumer.ssl.truststore.location=/var/private/ssl/kafka.server.truststore.jks database.history.consumer.ssl.truststore.password=test1234 database.history.consumer.ssl.key.password=test1234
Debezium strips the prefix from the property name before it passes the property to the Kafka client.
See the Kafka documentation for more details about Kafka producer configuration properties and Kafka consumer configuration properties.
Debezium connector pass-through database driver configuration properties
The Debezium connector provides for pass-through configuration of the database driver. Pass-through database properties begin with the prefix database.*
. For example, the connector passes properties such as database.foobar=false
to the JDBC URL.
As is the case with the pass-through properties for database history clients, Debezium strips the prefixes from the properties before it passes them to the database driver.
3.7. Monitoring Debezium Db2 connector performance
The Debezium Db2 connector provides three types of metrics that are in addition to the built-in support for JMX metrics that Apache ZooKeeper, Apache Kafka, and Kafka Connect provide.
- Snapshot metrics provide information about connector operation while performing a snapshot.
- Streaming metrics provide information about connector operation when the connector is capturing changes and streaming change event records.
- Schema history metrics provide information about the status of the connector’s schema history.
Debezium monitoring documentation provides details for how to expose these metrics by using JMX.
3.7.1. Monitoring Debezium during snapshots of Db2 databases
The MBean is debezium.db2:type=connector-metrics,context=snapshot,server=<db2.server.name>
.
Snapshot metrics are not exposed unless a snapshot operation is active, or if a snapshot has occurred since the last connector start.
The following table lists the shapshot metrics that are available.
Attributes | Type | Description |
---|---|---|
| The last snapshot event that the connector has read. | |
| The number of milliseconds since the connector has read and processed the most recent event. | |
| The total number of events that this connector has seen since last started or reset. | |
| The number of events that have been filtered by include/exclude list filtering rules configured on the connector. | |
|
| The list of tables that are monitored by the connector. |
| The list of tables that are captured by the connector. | |
| The length the queue used to pass events between the snapshotter and the main Kafka Connect loop. | |
| The free capacity of the queue used to pass events between the snapshotter and the main Kafka Connect loop. | |
| The total number of tables that are being included in the snapshot. | |
| The number of tables that the snapshot has yet to copy. | |
| Whether the snapshot was started. | |
| Whether the snapshot was aborted. | |
| Whether the snapshot completed. | |
| The total number of seconds that the snapshot has taken so far, even if not complete. | |
| Map containing the number of rows scanned for each table in the snapshot. Tables are incrementally added to the Map during processing. Updates every 10,000 rows scanned and upon completing a table. | |
|
The maximum buffer of the queue in bytes. It will be enabled if | |
| The current data of records in the queue in bytes. |
The connector also provides the following additional snapshot metrics when an incremental snapshot is executed:
Attributes | Type | Description |
---|---|---|
| The identifier of the current snapshot chunk. | |
| The lower bound of the primary key set defining the current chunk. | |
| The upper bound of the primary key set defining the current chunk. | |
| The lower bound of the primary key set of the currently snapshotted table. | |
| The upper bound of the primary key set of the currently snapshotted table. |
Incremental snapshots is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
3.7.2. Monitoring Debezium Db2 connector record streaming
The MBean is debezium.db2:type=connector-metrics,context=streaming,server=<db2.server.name>
.
The following table lists the streaming metrics that are available.
Attributes | Type | Description |
---|---|---|
| The last streaming event that the connector has read. | |
| The number of milliseconds since the connector has read and processed the most recent event. | |
| The total number of events that this connector has seen since last started or reset. | |
| The number of events that have been filtered by include/exclude list filtering rules configured on the connector. | |
|
| The list of tables that are monitored by the connector. |
| The list of tables that are captured by the connector. | |
| The length the queue used to pass events between the streamer and the main Kafka Connect loop. | |
| The free capacity of the queue used to pass events between the streamer and the main Kafka Connect loop. | |
| Flag that denotes whether the connector is currently connected to the database server. | |
| The number of milliseconds between the last change event’s timestamp and the connector processing it. The values will incoporate any differences between the clocks on the machines where the database server and the connector are running. | |
| The number of processed transactions that were committed. | |
| The coordinates of the last received event. | |
| Transaction identifier of the last processed transaction. | |
| The maximum buffer of the queue in bytes. | |
| The current data of records in the queue in bytes. |
3.7.3. Monitoring Debezium Db2 connector schema history
The MBean is debezium.db2:type=connector-metrics,context=schema-history,server=<db2.server.name>
.
The following table lists the schema history metrics that are available.
Attributes | Type | Description |
---|---|---|
|
One of | |
| The time in epoch seconds at what recovery has started. | |
| The number of changes that were read during recovery phase. | |
| the total number of schema changes applied during recovery and runtime. | |
| The number of milliseconds that elapsed since the last change was recovered from the history store. | |
| The number of milliseconds that elapsed since the last change was applied. | |
| The string representation of the last change recovered from the history store. | |
| The string representation of the last applied change. |
3.8. Managing Debezium Db2 connectors
After you deploy a Debezium Db2 connector, use the Debezium management UDFs to control Db2 replication (ASN) with SQL commands. Some of the UDFs expect a return value in which case you use the SQL VALUE
statement to invoke them. For other UDFs, use the SQL CALL
statement.
Task | Command and notes |
---|---|
| |
| |
| |
| |
| |
|
3.9. Updating schemas for Db2 tables in capture mode for Debezium connectors
While a Debezium Db2 connector can capture schema changes, to update a schema, you must collaborate with a database administrator to ensure that the connector continues to produce change events. This is required by the way that Db2 implements replication.
For each table in capture mode, Db2’s replication feature creates a change-data table that contains all changes to that source table. However, change-data table schemas are static. If you update the schema for a table in capture mode then you must also update the schema of its corresponding change-data table. A Debezium Db2 connector cannot do this. A database administrator with elevated privileges must update schemas for tables that are in capture mode.
It is vital to execute a schema update procedure completely before there is a new schema update on the same table. Consequently, the recommendation is to execute all DDLs in a single batch so the schema update procedure is done only once.
There are generally two procedures for updating table schemas:
Each approach has advantages and disadvantages.
3.9.1. Performing offline schema updates for Debezium Db2 connectors
You stop the Debezium Db2 connector before you perform an offline schema update. While this is the safer schema update procedure, it might not be feasible for applications with high-availability requirements.
Prerequisites
- One or more tables that are in capture mode require schema updates.
Procedure
- Suspend the application that updates the database.
- Wait for the Debezium connector to stream all unstreamed change event records.
- Stop the Debezium connector.
- Apply all changes to the source table schema.
-
In the ASN register table, mark the tables with updated schemas as
INACTIVE
. - Reinitialize the ASN capture service.
- Remove the source table with the old schema from capture mode by running the Debezium UDF for removing tables from capture mode.
- Add the source table with the new schema to capture mode by running the Debezium UDF for adding tables to capture mode.
-
In the ASN register table, mark the updated source tables as
ACTIVE
. - Reinitialize the ASN capture service.
- Resume the application that updates the database.
- Restart the Debezium connector.
3.9.2. Performing online schema updates for Debezium Db2 connectors
An online schema update does not require application and data processing downtime. That is, you do not stop the Debezium Db2 connector before you perform an online schema update. Also, an online schema update procedure is simpler than the procedure for an offline schema update.
However, when a table is in capture mode, after a change to a column name, the Db2 replication feature continues to use the old column name. The new column name does not appear in Debezium change events. You must restart the connector to see the new column name in change events.
Prerequisites
- One or more tables that are in capture mode require schema updates.
Procedure when adding a column to the end of a table
- Lock the source tables whose schema you want to change.
-
In the ASN register table, mark the locked tables as
INACTIVE
. - Reinitialize the ASN capture service.
- Apply all changes to the schemas for the source tables.
- Apply all changes to the schemas for the corresponding change-data tables.
-
In the ASN register table, mark the source tables as
ACTIVE
. - Reinitialize the ASN capture service.
- Optional. Restart the connector to see updated column names in change events.
Procedure when adding a column to the middle of a table
- Lock the source table(s) to be changed.
-
In the ASN register table, mark the locked tables as
INACTIVE
. - Reinitialize the ASN capture service.
For each source table to be changed:
- Export the data in the source table.
- Truncate the source table.
- Alter the source table and add the column.
- Load the exported data into the altered source table.
- Export the data in the source table’s corresponding change-data table.
- Truncate the change-data table.
- Alter the change-data table and add the column.
- Load the exported data into the altered change-data table.
-
In the ASN register table, mark the tables as
INACTIVE
. This marks the old change-data tables as inactive, which allows the data in them to remain but they are no longer updated. - Reinitialize the ASN capture service.
- Optional. Restart the connector to see updated column names in change events.
Chapter 4. Debezium connector for MongoDB
Debezium’s MongoDB connector tracks a MongoDB replica set or a MongoDB sharded cluster for document changes in databases and collections, recording those changes as events in Kafka topics. The connector automatically handles the addition or removal of shards in a sharded cluster, changes in membership of each replica set, elections within each replica set, and awaiting the resolution of communications problems.
For information about the MongoDB versions that are compatible with this connector, see the Debezium Supported Configurations page.
Information and procedures for using a Debezium MongoDB connector is organized as follows:
- Section 4.1, “Overview of Debezium MongoDB connector”
- Section 4.2, “How Debezium MongoDB connectors work”
- Section 4.3, “Descriptions of Debezium MongoDB connector data change events”
- Section 4.4, “Setting up MongoDB to work with a Debezium connector”
- Section 4.5, “Deployment of Debezium MongoDB connectors”
- Section 4.6, “Monitoring Debezium MongoDB connector performance”
- Section 4.7, “How Debezium MongoDB connectors handle faults and problems”
4.1. Overview of Debezium MongoDB connector
MongoDB’s replication mechanism provides redundancy and high availability, and is the preferred way to run MongoDB in production. MongoDB connector captures the changes in a replica set or sharded cluster.
A MongoDB replica set consists of a set of servers that all have copies of the same data, and replication ensures that all changes made by clients to documents on the replica set’s primary are correctly applied to the other replica set’s servers, called secondaries. MongoDB replication works by having the primary record the changes in its oplog (or operation log), and then each of the secondaries reads the primary’s oplog and applies in order all of the operations to their own documents. When a new server is added to a replica set, that server first performs an snapshot of all of the databases and collections on the primary, and then reads the primary’s oplog to apply all changes that might have been made since it began the snapshot. This new server becomes a secondary (and able to handle queries) when it catches up to the tail of the primary’s oplog.
The MongoDB connector uses this same replication mechanism, though it does not actually become a member of the replica set. Just like MongoDB secondaries, however, the connector always reads the oplog of the replica set’s primary. And, when the connector sees a replica set for the first time, it looks at the oplog to get the last recorded transaction and then performs a snapshot of the primary’s databases and collections. When all the data is copied, the connector then starts streaming changes from the position it read earlier from the oplog. Operations in the MongoDB oplog are idempotent, so no matter how many times the operations are applied, they result in the same end state.
As the MongoDB connector processes changes, it periodically records the position in the oplog where the event originated. When the MongoDB connector stops, it records the last oplog position that it processed, so that upon restart it simply begins streaming from that position. In other words, the connector can be stopped, upgraded or maintained, and restarted some time later, and it will pick up exactly where it left off without losing a single event. Of course, MongoDB’s oplogs are usually capped at a maximum size, which means that the connector should not be stopped for too long, or else some of the operations in the oplog might be purged before the connector has a chance to read them. In this case, upon restart the connector will detect the missing oplog operations, perform a snapshot, and then proceed with streaming the changes.
The MongoDB connector is also quite tolerant of changes in membership and leadership of the replica sets, of additions or removals of shards within a sharded cluster, and network problems that might cause communication failures. The connector always uses the replica set’s primary node to stream changes, so when the replica set undergoes an election and a different node becomes primary, the connector will immediately stop streaming changes, connect to the new primary, and start streaming changes using the new primary node. Likewise, if connector experiences any problems communicating with the replica set primary, it will try to reconnect (using exponential backoff so as to not overwhelm the network or replica set) and continue streaming changes from where it last left off. In this way the connector is able to dynamically adjust to changes in replica set membership and to automatically handle communication failures.
Additional resources
4.2. How Debezium MongoDB connectors work
An overview of the MongoDB topologies that the connector supports is useful for planning your application.
When a MongoDB connector is configured and deployed, it starts by connecting to the MongoDB servers at the seed addresses, and determines the details about each of the available replica sets. Since each replica set has its own independent oplog, the connector will try to use a separate task for each replica set. The connector can limit the maximum number of tasks it will use, and if not enough tasks are available the connector will assign multiple replica sets to each task, although the task will still use a separate thread for each replica set.
When running the connector against a sharded cluster, use a value of tasks.max
that is greater than the number of replica sets. This will allow the connector to create one task for each replica set, and will let Kafka Connect coordinate, distribute, and manage the tasks across all of the available worker processes.
The following topics provide details about how the Debezium MongoDB connector works:
- Section 4.2.1, “MongoDB topologies supported by Debezium connectors”
- Section 4.2.2, “How Debezium MongoDB connectors use logical names for replica sets and sharded clusters”
- Section 4.2.3, “How Debezium MongoDB connectors perform snapshots”
- Section 4.2.4, “How the Debezium MongoDB connector streams change event records”
- Section 4.2.5, “Default names of Kafka topics that receive Debezium MongoDB change event records”
- Section 4.2.6, “How event keys control topic partitioning for the Debezium MongoDB connector”
- Section 4.2.7, “Debezium MongoDB connector-generated events that represent transaction boundaries”
4.2.1. MongoDB topologies supported by Debezium connectors
The MongoDB connector supports the following MongoDB topologies:
- MongoDB replica set
The Debezium MongoDB connector can capture changes from a single MongoDB replica set. Production replica sets require a minimum of at least three members.
To use the MongoDB connector with a replica set, provide the addresses of one or more replica set servers as seed addresses through the connector’s
mongodb.hosts
property. The connector will use these seeds to connect to the replica set, and then once connected will get from the replica set the complete set of members and which member is primary. The connector will start a task to connect to the primary and capture the changes from the primary’s oplog. When the replica set elects a new primary, the task will automatically switch over to the new primary.NoteWhen MongoDB is fronted by a proxy (such as with Docker on OS X or Windows), then when a client connects to the replica set and discovers the members, the MongoDB client will exclude the proxy as a valid member and will attempt and fail to connect directly to the members rather than go through the proxy.
In such a case, set the connector’s optional
mongodb.members.auto.discover
configuration property tofalse
to instruct the connector to forgo membership discovery and instead simply use the first seed address (specified via themongodb.hosts
property) as the primary node. This may work, but still make cause issues when election occurs.
- MongoDB sharded cluster
A MongoDB sharded cluster consists of:
- One or more shards, each deployed as a replica set;
- A separate replica set that acts as the cluster’s configuration server
One or more routers (also called
mongos
) to which clients connect and that routes requests to the appropriate shardsTo use the MongoDB connector with a sharded cluster, configure the connector with the host addresses of the configuration server replica set. When the connector connects to this replica set, it discovers that it is acting as the configuration server for a sharded cluster, discovers the information about each replica set used as a shard in the cluster, and will then start up a separate task to capture the changes from each replica set. If new shards are added to the cluster or existing shards removed, the connector will automatically adjust its tasks accordingly.
- MongoDB standalone server
- The MongoDB connector is not capable of monitoring the changes of a standalone MongoDB server, since standalone servers do not have an oplog. The connector will work if the standalone server is converted to a replica set with one member.
MongoDB does not recommend running a standalone server in production. For more information, see the MongoDB documentation.
4.2.2. How Debezium MongoDB connectors use logical names for replica sets and sharded clusters
The connector configuration property mongodb.name
serves as a logical name for the MongoDB replica set or sharded cluster. The connector uses the logical name in a number of ways: as the prefix for all topic names, and as a unique identifier when recording the oplog position of each replica set.
You should give each MongoDB connector a unique logical name that meaningfully describes the source MongoDB system. We recommend logical names begin with an alphabetic or underscore character, and remaining characters that are alphanumeric or underscore.
4.2.3. How Debezium MongoDB connectors perform snapshots
When a task starts up using a replica set, it uses the connector’s logical name and the replica set name to find an offset that describes the position where the connector previously stopped reading changes. If an offset can be found and it still exists in the oplog, then the task immediately proceeds with streaming changes, starting at the recorded offset position.
However, if no offset is found or if the oplog no longer contains that position, the task must first obtain the current state of the replica set contents by performing a snapshot. This process starts by recording the current position of the oplog and recording that as the offset (along with a flag that denotes a snapshot has been started). The task will then proceed to copy each collection, spawning as many threads as possible (up to the value of the snapshot.max.threads
configuration property) to perform this work in parallel. The connector will record a separate read event for each document it sees, and that read event will contain the object’s identifier, the complete state of the object, and source information about the MongoDB replica set where the object was found. The source information will also include a flag that denotes the event was produced during a snapshot.
This snapshot will continue until it has copied all collections that match the connector’s filters. If the connector is stopped before the tasks' snapshots are completed, upon restart the connector begins the snapshot again.
Try to avoid task reassignment and reconfiguration while the connector is performing a snapshot of any replica sets. The connector does log messages with the progress of the snapshot. For utmost control, run a separate cluster of Kafka Connect for each connector.
4.2.4. How the Debezium MongoDB connector streams change event records
After the connector task for a replica set records an offset, it uses the offset to determine the position in the oplog where it should start streaming changes. The task then connects to the replica set’s primary node and start streaming changes from that position. It processes all of create, insert, and delete operations, and converts them into Debezium change events. Each change event includes the position in the oplog where the operation was found, and the connector periodically records this as its most recent offset. The interval at which the offset is recorded is governed by offset.flush.interval.ms
, which is a Kafka Connect worker configuration property.
When the connector is stopped gracefully, the last offset processed is recorded so that, upon restart, the connector will continue exactly where it left off. If the connector’s tasks terminate unexpectedly, however, then the tasks may have processed and generated events after it last records the offset but before the last offset is recorded; upon restart, the connector begins at the last recorded offset, possibly generating some the same events that were previously generated just prior to the crash.
When everything is operating nominally, Kafka consumers will actually see every message exactly once. However, when things go wrong Kafka can only guarantee consumers will see every message at least once. Therefore, your consumers need to anticipate seeing messages more than once.
As mentioned above, the connector tasks always use the replica set’s primary node to stream changes from the oplog, ensuring that the connector sees the most up-to-date operations as possible and can capture the changes with lower latency than if secondaries were to be used instead. When the replica set elects a new primary, the connector immediately stops streaming changes, connects to the new primary, and starts streaming changes from the new primary node at the same position. Likewise, if the connector experiences any problems communicating with the replica set members, it tries to reconnect, by using exponential backoff so as to not overwhelm the replica set, and once connected it continues streaming changes from where it last left off. In this way, the connector is able to dynamically adjust to changes in replica set membership and automatically handle communication failures.
To summarize, the MongoDB connector continues running in most situations. Communication problems might cause the connector to wait until the problems are resolved.
4.2.5. Default names of Kafka topics that receive Debezium MongoDB change event records
The MongoDB connector writes events for all insert, update, and delete operations to documents in each collection to a single Kafka topic. The name of the Kafka topics always takes the form logicalName.databaseName.collectionName, where logicalName is the logical name of the connector as specified with the mongodb.name
configuration property, databaseName is the name of the database where the operation occurred, and collectionName is the name of the MongoDB collection in which the affected document existed.
For example, consider a MongoDB replica set with an inventory
database that contains four collections: products
, products_on_hand
, customers
, and orders
. If the connector monitoring this database were given a logical name of fulfillment
, then the connector would produce events on these four Kafka topics:
-
fulfillment.inventory.products
-
fulfillment.inventory.products_on_hand
-
fulfillment.inventory.customers
-
fulfillment.inventory.orders
Notice that the topic names do not incorporate the replica set name or shard name. As a result, all changes to a sharded collection (where each shard contains a subset of the collection’s documents) all go to the same Kafka topic.
You can set up Kafka to auto-create the topics as they are needed. If not, then you must use Kafka administration tools to create the topics before starting the connector.
4.2.6. How event keys control topic partitioning for the Debezium MongoDB connector
The MongoDB connector does not make any explicit determination about how to partition topics for events. Instead, it allows Kafka to determine how to partition topics based on event keys. You can change Kafka’s partitioning logic by defining the name of the Partitioner
implementation in the Kafka Connect worker configuration.
Kafka maintains total order only for events written to a single topic partition. Partitioning the events by key does mean that all events with the same key always go to the same partition. This ensures that all events for a specific document are always totally ordered.
4.2.7. Debezium MongoDB connector-generated events that represent transaction boundaries
Debezium can generate events that represents transaction metadata boundaries and enrich change data event messages.
Debezium registers and receives metadata only for transactions that occur after you deploy the connector. Metadata for transactions that occur before you deploy the connector is not available.
For every transaction BEGIN
and END
, Debezium generates an event that contains the following fields:
status
-
BEGIN
orEND
id
- String representation of unique transaction identifier.
event_count
(forEND
events)- Total number of events emitted by the transaction.
data_collections
(forEND
events)-
An array of pairs of
data_collection
andevent_count
that provides number of events emitted by changes originating from given data collection.
The following example shows a typical message:
{ "status": "BEGIN", "id": "1462833718356672513", "event_count": null, "data_collections": null } { "status": "END", "id": "1462833718356672513", "event_count": 2, "data_collections": [ { "data_collection": "rs0.testDB.collectiona", "event_count": 1 }, { "data_collection": "rs0.testDB.collectionb", "event_count": 1 } ] }
Unless overridden via the transaction.topic
option, transaction events are written to the topic named database.server.name.transaction
.
Change data event enrichment
When transaction metadata is enabled, the data message Envelope
is enriched with a new transaction
field. This field provides information about every event in the form of a composite of fields:
id
- String representation of unique transaction identifier.
total_order
- The absolute position of the event among all events generated by the transaction.
data_collection_order
- The per-data collection position of the event among all events that were emitted by the transaction.
Following is an example of what a message looks like:
{ "patch": null, "after": "{\"_id\" : {\"$numberLong\" : \"1004\"},\"first_name\" : \"Anne\",\"last_name\" : \"Kretchmar\",\"email\" : \"annek@noanswer.org\"}", "source": { ... }, "op": "c", "ts_ms": "1580390884335", "transaction": { "id": "1462833718356672513", "total_order": "1", "data_collection_order": "1" } }
4.3. Descriptions of Debezium MongoDB connector data change events
The Debezium MongoDB connector generates a data change event for each document-level operation that inserts, updates, or deletes data. Each event contains a key and a value. The structure of the key and the value depends on the collection that was changed.
Debezium and Kafka Connect are designed around continuous streams of event messages. However, the structure of these events may change over time, which can be difficult for consumers to handle. To address this, each event contains the schema for its content or, if you are using a schema registry, a schema ID that a consumer can use to obtain the schema from the registry. This makes each event self-contained.
The following skeleton JSON shows the basic four parts of a change event. However, how you configure the Kafka Connect converter that you choose to use in your application determines the representation of these four parts in change events. A schema
field is in a change event only when you configure the converter to produce it. Likewise, the event key and event payload are in a change event only if you configure a converter to produce it. If you use the JSON converter and you configure it to produce all four basic change event parts, change events have this structure:
{ "schema": { 1 ... }, "payload": { 2 ... }, "schema": { 3 ... }, "payload": { 4 ... }, }
Item | Field name | Description |
---|---|---|
1 |
|
The first |
2 |
|
The first |
3 |
|
The second |
4 |
|
The second |
By default, the connector streams change event records to topics with names that are the same as the event’s originating collection. See topic names.
The MongoDB connector ensures that all Kafka Connect schema names adhere to the Avro schema name format. This means that the logical server name must start with a Latin letter or an underscore, that is, a-z, A-Z, or _. Each remaining character in the logical server name and each character in the database and collection names must be a Latin letter, a digit, or an underscore, that is, a-z, A-Z, 0-9, or \_. If there is an invalid character it is replaced with an underscore character.
This can lead to unexpected conflicts if the logical server name, a database name, or a collection name contains invalid characters, and the only characters that distinguish names from one another are invalid and thus replaced with underscores.
For more information, see the following topics:
4.3.1. About keys in Debezium MongoDB change events
A change event’s key contains the schema for the changed document’s key and the changed document’s actual key. For a given collection, both the schema and its corresponding payload contain a single id
field. The value of this field is the document’s identifier represented as a string that is derived from MongoDB extended JSON serialization strict mode.
Consider a connector with a logical name of fulfillment
, a replica set containing an inventory
database, and a customers
collection that contains documents such as the following.
Example document
{ "_id": 1004, "first_name": "Anne", "last_name": "Kretchmar", "email": "annek@noanswer.org" }
Example change event key
Every change event that captures a change to the customers
collection has the same event key schema. For as long as the customers
collection has the previous definition, every change event that captures a change to the customers
collection has the following key structure. In JSON, it looks like this:
{ "schema": { 1 "type": "struct", "name": "fulfillment.inventory.customers.Key", 2 "optional": false, 3 "fields": [ 4 { "field": "id", "type": "string", "optional": false } ] }, "payload": { 5 "id": "1004" } }
Item | Field name | Description |
---|---|---|
1 |
|
The schema portion of the key specifies a Kafka Connect schema that describes what is in the key’s |
2 |
|
Name of the schema that defines the structure of the key’s payload. This schema describes the structure of the key for the document that was changed. Key schema names have the format connector-name.database-name.collection-name.
|
3 |
|
Indicates whether the event key must contain a value in its |
4 |
|
Specifies each field that is expected in the |
5 |
|
Contains the key for the document for which this change event was generated. In this example, the key contains a single |
This example uses a document with an integer identifier, but any valid MongoDB document identifier works the same way, including a document identifier. For a document identifier, an event key’s payload.id
value is a string that represents the updated document’s original _id
field as a MongoDB extended JSON serialization that uses strict mode. The following table provides examples of how different types of _id
fields are represented.
Type | MongoDB _id Value | Key’s payload |
---|---|---|
Integer | 1234 |
|
Float | 12.34 |
|
String | "1234" |
|
Document |
|
|
ObjectId |
|
|
Binary |
|
|
4.3.2. About values in Debezium MongoDB change events
The value in a change event is a bit more complicated than the key. Like the key, the value has a schema
section and a payload
section. The schema
section contains the schema that describes the Envelope
structure of the payload
section, including its nested fields. Change events for operations that create, update or delete data all have a value payload with an envelope structure.
Consider the same sample document that was used to show an example of a change event key:
Example document
{ "_id": 1004, "first_name": "Anne", "last_name": "Kretchmar", "email": "annek@noanswer.org" }
The value portion of a change event for a change to this document is described for each event type:
create events
The following example shows the value portion of a change event that the connector generates for an operation that creates data in the customers
collection:
{ "schema": { 1 "type": "struct", "fields": [ { "type": "string", "optional": true, "name": "io.debezium.data.Json", 2 "version": 1, "field": "after" }, { "type": "string", "optional": true, "name": "io.debezium.data.Json", "version": 1, "field": "patch" }, { "type": "struct", "fields": [ { "type": "string", "optional": false, "field": "version" }, { "type": "string", "optional": false, "field": "connector" }, { "type": "string", "optional": false, "field": "name" }, { "type": "int64", "optional": false, "field": "ts_ms" }, { "type": "boolean", "optional": true, "default": false, "field": "snapshot" }, { "type": "string", "optional": false, "field": "db" }, { "type": "string", "optional": false, "field": "rs" }, { "type": "string", "optional": false, "field": "collection" }, { "type": "int32", "optional": false, "field": "ord" }, { "type": "int64", "optional": true, "field": "h" } ], "optional": false, "name": "io.debezium.connector.mongo.Source", 3 "field": "source" }, { "type": "string", "optional": true, "field": "op" }, { "type": "int64", "optional": true, "field": "ts_ms" } ], "optional": false, "name": "dbserver1.inventory.customers.Envelope" 4 }, "payload": { 5 "after": "{\"_id\" : {\"$numberLong\" : \"1004\"},\"first_name\" : \"Anne\",\"last_name\" : \"Kretchmar\",\"email\" : \"annek@noanswer.org\"}", 6 "patch": null, "source": { 7 "version": "1.7.2.Final", "connector": "mongodb", "name": "fulfillment", "ts_ms": 1558965508000, "snapshot": false, "db": "inventory", "rs": "rs0", "collection": "customers", "ord": 31, "h": 1546547425148721999 }, "op": "c", 8 "ts_ms": 1558965515240 9 } }
Item | Field name | Description |
---|---|---|
1 |
| The value’s schema, which describes the structure of the value’s payload. A change event’s value schema is the same in every change event that the connector generates for a particular collection. |
2 |
|
In the |
3 |
|
|
4 |
|
|
5 |
|
The value’s actual data. This is the information that the change event is providing. |
6 |
|
An optional field that specifies the state of the document after the event occurred. In this example, the |
7 |
| Mandatory field that describes the source metadata for the event. This field contains information that you can use to compare this event with other events, with regard to the origin of the events, the order in which the events occurred, and whether events were part of the same transaction. The source metadata includes:
|
8 |
|
Mandatory string that describes the type of operation that caused the connector to generate the event. In this example,
|
9 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
update events
The value of a change event for an update in the sample customers
collection has the same schema as a create event for that collection. Likewise, the event value’s payload has the same structure. However, the event value payload contains different values in an update event. An update event does not have an after
value. Instead, it has these two fields:
-
patch
is a string field that contains the JSON representation of the idempotent update operation -
filter
is a string field that contains the JSON representation of the selection criteria for the update. Thefilter
string can include multiple shard key fields for sharded collections.
Here is an example of a change event value in an event that the connector generates for an update in the customers
collection:
{ "schema": { ... }, "payload": { "op": "u", 1 "ts_ms": 1465491461815, 2 "patch": "{\"$set\":{\"first_name\":\"Anne Marie\"}}", 3 "filter": "{\"_id\" : {\"$numberLong\" : \"1004\"}}", 4 "source": { 5 "version": "1.7.2.Final", "connector": "mongodb", "name": "fulfillment", "ts_ms": 1558965508000, "snapshot": true, "db": "inventory", "rs": "rs0", "collection": "customers", "ord": 6, "h": 1546547425148721999 } } }
Item | Field name | Description |
---|---|---|
1 |
|
Mandatory string that describes the type of operation that caused the connector to generate the event. In this example, |
2 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
3 |
|
Contains the JSON string representation of the actual MongoDB idempotent change to the document. In this example, the update changed the |
4 |
| Contains the JSON string representation of the MongoDB selection criteria that was used to identify the document to be updated. |
5 |
| Mandatory field that describes the source metadata for the event. This field contains the same information as a create event for the same collection, but the values are different since this event is from a different position in the oplog. The source metadata includes:
|
In a Debezium change event, MongoDB provides the content of the patch
field. The format of this field depends on the version of the MongoDB database. Consequently, be prepared for potential changes to the format when you upgrade to a newer MongoDB database version. Examples in this document were obtained from MongoDB 3.4, In your application, event formats might be different.
In MongoDB’s oplog, update events do not contain the before or after states of the changed document. Consequently, it is not possible for a Debezium connector to provide this information. However, a Debezium connector provides a document’s starting state in create and read events. Downstream consumers of the stream can reconstruct document state by keeping the latest state for each document and comparing the state in a new event with the saved state. Debezium connector’s are not able to keep this state.
delete events
The value in a delete change event has the same schema
portion as create and update events for the same collection. The payload
portion in a delete event contains values that are different from create and update events for the same collection. In particular, a delete event contains neither an after
value nor a patch
value. Here is an example of a delete event for a document in the customers
collection:
{ "schema": { ... }, "payload": { "op": "d", 1 "ts_ms": 1465495462115, 2 "filter": "{\"_id\" : {\"$numberLong\" : \"1004\"}}", 3 "source": { 4 "version": "1.7.2.Final", "connector": "mongodb", "name": "fulfillment", "ts_ms": 1558965508000, "snapshot": true, "db": "inventory", "rs": "rs0", "collection": "customers", "ord": 6, "h": 1546547425148721999 } } }
Item | Field name | Description |
---|---|---|
1 |
|
Mandatory string that describes the type of operation. The |
2 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
3 |
| Contains the JSON string representation of the MongoDB selection criteria that was used to identify the document to be deleted. |
4 |
| Mandatory field that describes the source metadata for the event. This field contains the same information as a create or update event for the same collection, but the values are different since this event is from a different position in the oplog. The source metadata includes:
|
MongoDB connector events are designed to work with Kafka log compaction. Log compaction enables removal of some older messages as long as at least the most recent message for every key is kept. This lets Kafka reclaim storage space while ensuring that the topic contains a complete data set and can be used for reloading key-based state.
Tombstone events
All MongoDB connector events for a uniquely identified document have exactly the same key. When a document is deleted, the delete event value still works with log compaction because Kafka can remove all earlier messages that have that same key. However, for Kafka to remove all messages that have that key, the message value must be null
. To make this possible, after Debezium’s MongoDB connector emits a delete event, the connector emits a special tombstone event that has the same key but a null
value. A tombstone event informs Kafka that all messages with that same key can be removed.
4.4. Setting up MongoDB to work with a Debezium connector
The MongoDB connector uses MongoDB’s oplog to capture the changes, so the connector works only with MongoDB replica sets or with sharded clusters where each shard is a separate replica set. See the MongoDB documentation for setting up a replica set or sharded cluster. Also, be sure to understand how to enable access control and authentication with replica sets.
You must also have a MongoDB user that has the appropriate roles to read the admin
database where the oplog can be read. Additionally, the user must also be able to read the config
database in the configuration server of a sharded cluster and must have listDatabases
privilege action.
4.5. Deployment of Debezium MongoDB connectors
You can use either of the following methods to deploy a Debezium MongoDB connector:
Additional resources
4.5.1. MongoDB connector deployment using AMQ Streams
Beginning with Debezium 1.7, the preferred method for deploying a Debezium connector is to use AMQ Streams to build a Kafka Connect container image that includes the connector plug-in.
During the deployment process, you create and use the following custom resources (CRs):
-
A
KafkaConnect
CR that defines your Kafka Connect instance and includes information about the connector artifacts needs to include in the image. -
A
KafkaConnector
CR that provides details that include information the connector uses to access the source database. After AMQ Streams starts the Kafka Connect pod, you start the connector by applying theKafkaConnector
CR.
In the build specification for the Kafka Connect image, you can specify the connectors that are available to deploy. For each connector plug-in, you can also specify other components that you want to make available for deployment. For example, you can add Service Registry artifacts, or the Debezium scripting component. When AMQ Streams builds the Kafka Connect image, it downloads the specified artifacts, and incorporates them into the image.
The spec.build.output
parameter in the KafkaConnect
CR specifies where to store the resulting Kafka Connect container image. Container images can be stored in a Docker registry, or in an OpenShift ImageStream. To store images in an ImageStream, you must create the ImageStream before you deploy Kafka Connect. ImageStreams are not created automatically.
If you use a KafkaConnect
resource to create a cluster, afterwards you cannot use the Kafka Connect REST API to create or update connectors. You can still use the REST API to retrieve information.
Additional resources
- Configuring Kafka Connect in Using AMQ Streams on OpenShift.
- Creating a new container image automatically using AMQ Streams in Deploying and Upgrading AMQ Streams on OpenShift.
4.5.2. Using AMQ Streams to deploy a Debezium MongoDB connector
With earlier versions of AMQ Streams, to deploy Debezium connectors on OpenShift, it was necessary to first build a Kafka Connect image for the connector. The current preferred method for deploying connectors on OpenShift is to use a build configuration in AMQ Streams to automatically build a Kafka Connect container image that includes the Debezium connector plug-ins that you want to use.
During the build process, the AMQ Streams Operator transforms input parameters in a KafkaConnect
custom resource, including Debezium connector definitions, into a Kafka Connect container image. The build downloads the necessary artifacts from the Red Hat Maven repository or another configured HTTP server. The newly created container is pushed to the container registry that is specified in .spec.build.output
, and is used to deploy a Kafka Connect pod. After AMQ Streams builds the Kafka Connect image, you create KafkaConnector
custom resources to start the connectors that are included in the build.
Prerequisites
- You have access to an OpenShift cluster on which the cluster Operator is installed.
- The AMQ Streams Operator is running.
- An Apache Kafka cluster is deployed as documented in Deploying and Upgrading AMQ Streams on OpenShift.
- You have a Red Hat Integration license.
- Kafka Connect is deployed on AMQ Streams.
-
The OpenShift
oc
CLI client is installed or you have access to the OpenShift Container Platform web console. Depending on how you intend to store the Kafka Connect build image, you need registry permissions or you must create an ImageStream resource:
- To store the build image in an image registry, such as Red Hat Quay.io or Docker Hub
- An account and permissions to create and manage images in the registry.
- To store the build image as a native OpenShift ImageStream
- An ImageStream resource is deployed to the cluster. You must explicitly create an ImageStream for the cluster. ImageStreams are not available by default.
Procedure
- Log in to the OpenShift cluster.
Create a Debezium
KafkaConnect
custom resource (CR) for the connector, or modify an existing one. For example, create aKafkaConnect
CR that specifies themetadata.annotations
andspec.build
properties, as shown in the following example. Save the file with a name such asdbz-connect.yaml
.Example 4.1. A
dbz-connect.yaml
file that defines aKafkaConnect
custom resource that includes a Debezium connectorapiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnect metadata: name: debezium-kafka-connect-cluster annotations: strimzi.io/use-connector-resources: "true" 1 spec: version: 3.00 build: 2 output: 3 type: imagestream 4 image: debezium-streams-connect:latest plugins: 5 - name: debezium-connector-mongodb artifacts: - type: zip 6 url: https://maven.repository.redhat.com/ga/io/debezium/debezium-connector-mongodb/1.7.2.Final-redhat-<build_number>/debezium-connector-mongodb-1.7.2.Final-redhat-<build_number>-plugin.zip 7 - type: zip url: https://maven.repository.redhat.com/ga/io/apicurio/apicurio-registry-distro-connect-converter/2.0-redhat-<build-number>/apicurio-registry-distro-connect-converter-2.0-redhat-<build-number>.zip - type: zip url: https://maven.repository.redhat.com/ga/io/debezium/debezium-scripting/1.7.2.Final/debezium-scripting-1.7.2.Final.zip bootstrapServers: debezium-kafka-cluster-kafka-bootstrap:9093
Table 4.7. Descriptions of Kafka Connect configuration settings Item Description 1
Sets the
strimzi.io/use-connector-resources
annotation to"true"
to enable the Cluster Operator to useKafkaConnector
resources to configure connectors in this Kafka Connect cluster.2
The
spec.build
configuration specifies where to store the build image and lists the plug-ins to include in the image, along with the location of the plug-in artifacts.3
The
build.output
specifies the registry in which the newly built image is stored.4
Specifies the name and image name for the image output. Valid values for
output.type
aredocker
to push into a container registry like Docker Hub or Quay, orimagestream
to push the image to an internal OpenShift ImageStream. To use an ImageStream, an ImageStream resource must be deployed to the cluster. For more information about specifying thebuild.output
in the KafkaConnect configuration, see the AMQ Streams Build schema reference documentation.5
The
plugins
configuration lists all of the connectors that you want to include in the Kafka Connect image. For each entry in the list, specify a plug-inname
, and information for about the artifacts that are required to build the connector. Optionally, for each connector plug-in, you can include other components that you want to be available for use with the connector. For example, you can add Service Registry artifacts, or the Debezium scripting component.6
The value of
artifacts.type
specifies the file type of the artifact specified in theartifacts.url
. Valid types arezip
,tgz
, orjar
. Debezium connector archives are provided in.zip
file format. JDBC driver files are in.jar
format. Thetype
value must match the type of the file that is referenced in theurl
field.7
The value of
artifacts.url
specifies the address of an HTTP server, such as a Maven repository, that stores the file for the connector artifact. The OpenShift cluster must have access to the specified server.Apply the
KafkaConnect
build specification to the OpenShift cluster by entering the following command:oc create -f dbz-connect.yaml
Based on the configuration specified in the custom resource, the Streams Operator prepares a Kafka Connect image to deploy.
After the build completes, the Operator pushes the image to the specified registry or ImageStream, and starts the Kafka Connect cluster. The connector artifacts that you listed in the configuration are available in the cluster.Create a
KafkaConnector
resource to define an instance of each connector that you want to deploy.
For example, create the followingKafkaConnector
CR, and save it asmongodb-inventory-connector.yaml
Example 4.2. A
mongodb-inventory-connector.yaml
file that defines theKafkaConnector
custom resource for a Debezium connectorapiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnector metadata: labels: strimzi.io/cluster: debezium-kafka-connect-cluster name: inventory-connector-mongodb 1 spec: class: io.debezium.connector.mongodb.MongoDbConnector 2 tasksMax: 1 3 config: 4 database.history.kafka.bootstrap.servers: 'debezium-kafka-cluster-kafka-bootstrap.debezium.svc.cluster.local:9092' database.history.kafka.topic: schema-changes.inventory database.hostname: mongodb.debezium-mongodb.svc.cluster.local 5 database.port: 3306 6 database.user: debezium 7 database.password: dbz 8 database.dbname: mydatabase 9 database.server.name: inventory_connector_mongodb 10 database.include.list: public.inventory 11
Table 4.8. Descriptions of connector configuration settings Item Description 1
The name of the connector to register with the Kafka Connect cluster.
2
The name of the connector class.
3
The number of tasks that can operate concurrently.
4
The connector’s configuration.
5
The address of the host database instance.
6
The port number of the database instance.
7
The name of the user account through which Debezium connects to the database.
8
The password for the database user account.
9
The name of the database to capture changes from.
10
The logical name of the database instance or cluster.
The specified name must be formed only from alphanumeric characters or underscores.
Because the logical name is used as the prefix for any Kafka topics that receive change events from this connector, the name must be unique among the connectors in the cluster.
The namespace is also used in the names of related Kafka Connect schemas, and the namespaces of a corresponding Avro schema if you integrate the connector with the Avro connector.11
The list of tables from which the connector captures change events.
Create the connector resource by running the following command:
oc create -n <namespace> -f <kafkaConnector>.yaml
For example,
oc create -n debezium -f {context}-inventory-connector.yaml
The connector is registered to the Kafka Connect cluster and starts to run against the database that is specified by
spec.config.database.dbname
in theKafkaConnector
CR. After the connector pod is ready, Debezium is running.
You are now ready to verify the Debezium MongoDB deployment.
4.5.3. Deploying a Debezium MongoDB connector by building a custom Kafka Connect container image from a Dockerfile
To deploy a Debezium MongoDB connector, you must build a custom Kafka Connect container image that contains the Debezium connector archive and then push this container image to a container registry. You then create two custom resources (CRs):
-
A
KafkaConnect
CR that defines your Kafka Connect instance. Theimage
property in the CR specifies the name of the container image that you create to run your Debezium connector. You apply this CR to the OpenShift instance where Red Hat AMQ Streams is deployed. AMQ Streams offers operators and images that bring Apache Kafka to OpenShift. -
A
KafkaConnector
CR that defines your Debezium MongoDB connector. Apply this CR to the same OpenShift instance where you apply theKafkaConnect
CR.
Prerequisites
- MongoDB is running and you completed the steps to set up MongoDB to work with a Debezium connector.
- AMQ Streams is deployed on OpenShift and is running Apache Kafka and Kafka Connect. For more information, see Deploying and Upgrading AMQ Streams on OpenShift.
- Podman or Docker is installed.
-
You have an account and permissions to create and manage containers in the container registry (such as
quay.io
ordocker.io
) to which you plan to add the container that will run your Debezium connector.
Procedure
Create the Debezium MongoDB container for Kafka Connect:
- Download the Debezium MongoDB connector archive.
Extract the Debezium MongoDB connector archive to create a directory structure for the connector plug-in, for example:
./my-plugins/ ├── debezium-connector-mongodb │ ├── ...
Create a Dockerfile that uses
registry.redhat.io/amq7/amq-streams-kafka-30-rhel8:2.0.0
as the base image. For example, from a terminal window, enter the following, replacingmy-plugins
with the name of your plug-ins directory:cat <<EOF >debezium-container-for-mongodb.yaml 1 FROM registry.redhat.io/amq7/amq-streams-kafka-30-rhel8:2.0.0 USER root:root COPY ./<my-plugins>/ /opt/kafka/plugins/ 2 USER 1001 EOF
The command creates a Dockerfile with the name
debezium-container-for-mongodb.yaml
in the current directory.Build the container image from the
debezium-container-for-mongodb.yaml
Docker file that you created in the previous step. From the directory that contains the file, open a terminal window and enter one of the following commands:podman build -t debezium-container-for-mongodb:latest .
docker build -t debezium-container-for-mongodb:latest .
The preceding commands build a container image with the name
debezium-container-for-mongodb
.Push your custom image to a container registry, such as
quay.io
or an internal container registry. The container registry must be available to the OpenShift instance where you want to deploy the image. Enter one of the following commands:podman push <myregistry.io>/debezium-container-for-mongodb:latest
docker push <myregistry.io>/debezium-container-for-mongodb:latest
Create a new Debezium MongoDB
KafkaConnect
custom resource (CR). For example, create aKafkaConnect
CR with the namedbz-connect.yaml
that specifiesannotations
andimage
properties as shown in the following example:apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnect metadata: name: my-connect-cluster annotations: strimzi.io/use-connector-resources: "true" 1 spec: #... image: debezium-container-for-mongodb 2
- 1
metadata.annotations
indicates to the Cluster Operator thatKafkaConnector
resources are used to configure connectors in this Kafka Connect cluster.- 2
spec.image
specifies the name of the image that you created to run your Debezium connector. This property overrides theSTRIMZI_DEFAULT_KAFKA_CONNECT_IMAGE
variable in the Cluster Operator.
Apply the
KafkaConnect
CR to the OpenShift Kafka Connect environment by entering the following command:oc create -f dbz-connect.yaml
The command adds a Kafka Connect instance that specifies the name of the image that you created to run your Debezium connector.
Create a
KafkaConnector
custom resource that configures your Debezium MongoDB connector instance.You configure a Debezium MongoDB connector in a
.yaml
file that specifies the configuration properties for the connector. The connector configuration might instruct Debezium to produce change events for a subset of MongoDB replica sets or sharded clusters. Optionally, you can set properties that filter out collections that are not needed.The following example configures a Debezium connector that connects to a MongoDB replica set
rs0
at port27017
on192.168.99.100
, and captures changes that occur in theinventory
collection.fullfillment
is the logical name of the replica set.MongoDB
inventory-connector.yaml
apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaConnector metadata: name: inventory-connector 1 labels: strimzi.io/cluster: my-connect-cluster spec: class: io.debezium.connector.mongodb.MongoDbConnector 2 config: mongodb.hosts: rs0/192.168.99.100:27017 3 mongodb.name: fulfillment 4 collection.include.list: inventory[.]* 5
- 1
- The name that is used to register the connector with Kafka Connect.
- 2
- The name of the MongoDB connector class.
- 3
- The host addresses to use to connect to the MongoDB replica set.
- 4
- The logical name of the MongoDB replica set, which forms a namespace for generated events and is used in all the names of the Kafka topics to which the connector writes, the Kafka Connect schema names, and the namespaces of the corresponding Avro schema when the Avro converter is used.
- 5
- An optional list of regular expressions that match the collection namespaces (for example, <dbName>.<collectionName>) of all collections to be monitored.
Create your connector instance with Kafka Connect. For example, if you saved your
KafkaConnector
resource in theinventory-connector.yaml
file, you would run the following command:oc apply -f inventory-connector.yaml
The preceding command registers
inventory-connector
and the connector starts to run against theinventory
collection as defined in theKafkaConnector
CR.
For the complete list of the configuration properties that you can set for the Debezium MongoDB connector, see MongoDB connector configuration properties.
Results
After the connector starts, it completes the following actions:
- Performs a consistent snapshot of the collections in your MongoDB replica sets.
- Reads the oplogs for the replica sets.
- Produces change events for every inserted, updated, and deleted document.
- Streams change event records to Kafka topics.
4.5.4. Verifying that the Debezium MongoDB connector is running
If the connector starts correctly without errors, it creates a topic for each table that the connector is configured to capture. Downstream applications can subscribe to these topics to retrieve information events that occur in the source database.
To verify that the connector is running, you perform the following operations from the OpenShift Container Platform web console, or through the OpenShift CLI tool (oc):
- Verify the connector status.
- Verify that the connector generates topics.
- Verify that topics are populated with events for read operations ("op":"r") that the connector generates during the initial snapshot of each table.
Prerequisites
- A Debezium connector is deployed to AMQ Streams on OpenShift.
-
The OpenShift
oc
CLI client is installed. - You have access to the OpenShift Container Platform web console.
Procedure
Check the status of the
KafkaConnector
resource by using one of the following methods:From the OpenShift Container Platform web console:
- Navigate to Home → Search.
-
On the Search page, click Resources to open the Select Resource box, and then type
KafkaConnector
. - From the KafkaConnectors list, click the name of the connector that you want to check, for example inventory-connector-mongodb.
- In the Conditions section, verify that the values in the Type and Status columns are set to Ready and True.
From a terminal window:
Enter the following command:
oc describe KafkaConnector <connector-name> -n <project>
For example,
oc describe KafkaConnector inventory-connector-mongodb -n debezium
The command returns status information that is similar to the following output:
Example 4.3.
KafkaConnector
resource statusName: inventory-connector-mongodb Namespace: debezium Labels: strimzi.io/cluster=debezium-kafka-connect-cluster Annotations: <none> API Version: kafka.strimzi.io/v1beta2 Kind: KafkaConnector ... Status: Conditions: Last Transition Time: 2021-12-08T17:41:34.897153Z Status: True Type: Ready Connector Status: Connector: State: RUNNING worker_id: 10.131.1.124:8083 Name: inventory-connector-mongodb Tasks: Id: 0 State: RUNNING worker_id: 10.131.1.124:8083 Type: source Observed Generation: 1 Tasks Max: 1 Topics: inventory_connector_mongodb inventory_connector_mongodb.inventory.addresses inventory_connector_mongodb.inventory.customers inventory_connector_mongodb.inventory.geom inventory_connector_mongodb.inventory.orders inventory_connector_mongodb.inventory.products inventory_connector_mongodb.inventory.products_on_hand Events: <none>
Verify that the connector created Kafka topics:
From the OpenShift Container Platform web console.
- Navigate to Home → Search.
-
On the Search page, click Resources to open the Select Resource box, and then type
KafkaTopic
. - From the KafkaTopics list, click the name of the topic that you want to check, for example, inventory-connector-mongodb.inventory.orders---ac5e98ac6a5d91e04d8ec0dc9078a1ece439081d.
- In the Conditions section, verify that the values in the Type and Status columns are set to Ready and True.
From a terminal window:
Enter the following command:
oc get kafkatopics
The command returns status information that is similar to the following output:
Example 4.4.
KafkaTopic
resource statusNAME CLUSTER PARTITIONS REPLICATION FACTOR READY connect-cluster-configs debezium-kafka-cluster 1 1 True connect-cluster-offsets debezium-kafka-cluster 25 1 True connect-cluster-status debezium-kafka-cluster 5 1 True consumer-offsets---84e7a678d08f4bd226872e5cdd4eb527fadc1c6a debezium-kafka-cluster 50 1 True inventory-connector-mongodb---a96f69b23d6118ff415f772679da623fbbb99421 debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.addresses---1b6beaf7b2eb57d177d92be90ca2b210c9a56480 debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.customers---9931e04ec92ecc0924f4406af3fdace7545c483b debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.geom---9f7e136091f071bf49ca59bf99e86c713ee58dd5 debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.orders---ac5e98ac6a5d91e04d8ec0dc9078a1ece439081d debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.products---df0746db116844cee2297fab611c21b56f82dcef debezium-kafka-cluster 1 1 True inventory-connector-mongodb.inventory.products-on-hand---8649e0f17ffcc9212e266e31a7aeea4585e5c6b5 debezium-kafka-cluster 1 1 True schema-changes.inventory debezium-kafka-cluster 1 1 True strimzi-store-topic---effb8e3e057afce1ecf67c3f5d8e4e3ff177fc55 debezium-kafka-cluster 1 1 True strimzi-topic-operator-kstreams-topic-store-changelog---b75e702040b99be8a9263134de3507fc0cc4017b debezium-kafka-cluster 1 1 True
Check topic content.
- From a terminal window, enter the following command:
oc exec -n <project> -it <kafka-cluster> -- /opt/kafka/bin/kafka-console-consumer.sh \ > --bootstrap-server localhost:9092 \ > --from-beginning \ > --property print.key=true \ > --topic=<topic-name>
For example,
oc exec -n debezium -it debezium-kafka-cluster-kafka-0 -- /opt/kafka/bin/kafka-console-consumer.sh \ > --bootstrap-server localhost:9092 \ > --from-beginning \ > --property print.key=true \ > --topic=inventory_connector_mongodb.inventory.products_on_hand
The format for specifying the topic name is the same as the
oc describe
command returns in Step 1, for example,inventory_connector_mongodb.inventory.addresses
.For each event in the topic, the command returns information that is similar to the following output:
Example 4.5. Content of a Debezium change event
{"schema":{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"}],"optional":false,"name":"inventory_connector_mongodb.inventory.products_on_hand.Key"},"payload":{"product_id":101}} {"schema":{"type":"struct","fields":[{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"},{"type":"int32","optional":false,"field":"quantity"}],"optional":true,"name":"inventory_connector_mongodb.inventory.products_on_hand.Value","field":"before"},{"type":"struct","fields":[{"type":"int32","optional":false,"field":"product_id"},{"type":"int32","optional":false,"field":"quantity"}],"optional":true,"name":"inventory_connector_mongodb.inventory.products_on_hand.Value","field":"after"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"version"},{"type":"string","optional":false,"field":"connector"},{"type":"string","optional":false,"field":"name"},{"type":"int64","optional":false,"field":"ts_ms"},{"type":"string","optional":true,"name":"io.debezium.data.Enum","version":1,"parameters":{"allowed":"true,last,false"},"default":"false","field":"snapshot"},{"type":"string","optional":false,"field":"db"},{"type":"string","optional":true,"field":"sequence"},{"type":"string","optional":true,"field":"table"},{"type":"int64","optional":false,"field":"server_id"},{"type":"string","optional":true,"field":"gtid"},{"type":"string","optional":false,"field":"file"},{"type":"int64","optional":false,"field":"pos"},{"type":"int32","optional":false,"field":"row"},{"type":"int64","optional":true,"field":"thread"},{"type":"string","optional":true,"field":"query"}],"optional":false,"name":"io.debezium.connector.mongodb.Source","field":"source"},{"type":"string","optional":false,"field":"op"},{"type":"int64","optional":true,"field":"ts_ms"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"id"},{"type":"int64","optional":false,"field":"total_order"},{"type":"int64","optional":false,"field":"data_collection_order"}],"optional":true,"field":"transaction"}],"optional":false,"name":"inventory_connector_mongodb.inventory.products_on_hand.Envelope"},"payload":{"before":null,"after":{"product_id":101,"quantity":3},"source":{"version":"1.7.2.Final-redhat-00001","connector":"mongodb","name":"inventory_connector_mongodb","ts_ms":1638985247805,"snapshot":"true","db":"inventory","sequence":null,"table":"products_on_hand","server_id":0,"gtid":null,"file":"mongodb-bin.000003","pos":156,"row":0,"thread":null,"query":null},"op":"r","ts_ms":1638985247805,"transaction":null}}
In the preceding example, the
payload
value shows that the connector snapshot generated a read ("op" ="r"
) event from the tableinventory.products_on_hand
. The"before"
state of theproduct_id
record isnull
, indicating that no previous value exists for the record. The"after"
state shows aquantity
of3
for the item withproduct_id
101
.
4.5.5. Description of Debezium Db2 connector configuration properties
The Debezium MongoDB connector has numerous configuration properties that you can use to achieve the right connector behavior for your application. Many properties have default values. Information about the properties is organized as follows:
The following configuration properties are required unless a default value is available.
Property | Default | Description |
---|---|---|
Unique name for the connector. Attempting to register again with the same name will fail. (This property is required by all Kafka Connect connectors.) | ||
The name of the Java class for the connector. Always use a value of | ||
The comma-separated list of hostname and port pairs (in the form 'host' or 'host:port') of the MongoDB servers in the replica set. The list can contain a single hostname and port pair. If | ||
A unique name that identifies the connector and/or MongoDB replica set or sharded cluster that this connector monitors. Each server should be monitored by at most one Debezium connector, since this server name prefixes all persisted Kafka topics emanating from the MongoDB replica set or cluster. Only alphanumeric characters, hyphens, dots and underscores must be used. | ||
Name of the database user to be used when connecting to MongoDB. This is required only when MongoDB is configured to use authentication. | ||
Password to be used when connecting to MongoDB. This is required only when MongoDB is configured to use authentication. | ||
|
Database (authentication source) containing MongoDB credentials. This is required only when MongoDB is configured to use authentication with another authentication database than | |
| Connector will use SSL to connect to MongoDB instances. | |
|
When SSL is enabled this setting controls whether strict hostname checking is disabled during connection phase. If | |
empty string |
An optional comma-separated list of regular expressions that match database names to be monitored; any database name not included in | |
empty string |
An optional comma-separated list of regular expressions that match database names to be excluded from monitoring; any database name not included in | |
empty string |
An optional comma-separated list of regular expressions that match fully-qualified namespaces for MongoDB collections to be monitored; any collection not included in | |
empty string |
An optional comma-separated list of regular expressions that match fully-qualified namespaces for MongoDB collections to be excluded from monitoring; any collection not included in | |
| Specifies the criteria for running a snapshot upon startup of the connector. The default is initial, and specifies the connector reads a snapshot when either no offset is found or if the oplog no longer contains the previous offset. The never option specifies that the connector should never use snapshots, instead the connector should proceed to tail the log. | |
All collections specified in |
An optional, comma-separated list of regular expressions that match names of schemas specified in | |
empty string | An optional comma-separated list of the fully-qualified names of fields that should be excluded from change event message values. Fully-qualified names for fields are of the form databaseName.collectionName.fieldName.nestedFieldName, where databaseName and collectionName may contain the wildcard (*) which matches any characters. | |
empty string | An optional comma-separated list of the fully-qualified replacements of fields that should be used to rename fields in change event message values. Fully-qualified replacements for fields are of the form databaseName.collectionName.fieldName.nestedFieldName:newNestedFieldName, where databaseName and collectionName may contain the wildcard (*) which matches any characters, the colon character (:) is used to determine rename mapping of field. The next field replacement is applied to the result of the previous field replacement in the list, so keep this in mind when renaming multiple fields that are in the same path. | |
| The maximum number of tasks that should be created for this connector. The MongoDB connector will attempt to use a separate task for each replica set, so the default is acceptable when using the connector with a single MongoDB replica set. When using the connector with a MongoDB sharded cluster, we recommend specifying a value that is equal to or more than the number of shards in the cluster, so that the work for each replica set can be distributed by Kafka Connect. | |
| Positive integer value that specifies the maximum number of threads used to perform an intial sync of the collections in a replica set. Defaults to 1. | |
|
Controls whether a delete event is followed by a tombstone event. | |
An interval in milliseconds that the connector should wait before taking a snapshot after starting up; | ||
|
Specifies the maximum number of documents that should be read in one go from each collection while taking a snapshot. The connector will read the collection contents in multiple batches of this size. |
The following advanced configuration properties have good defaults that will work in most situations and therefore rarely need to be specified in the connector’s configuration.
Property | Default | Description |
---|---|---|
|
Positive integer value that specifies the maximum size of the blocking queue into which change events read from the database log are placed before they are written to Kafka. This queue can provide backpressure to the oplog reader when, for example, writes to Kafka are slower or if Kafka is not available. Events that appear in the queue are not included in the offsets periodically recorded by this connector. Defaults to 8192, and should always be larger than the maximum batch size specified in the | |
| Positive integer value that specifies the maximum size of each batch of events that should be processed during each iteration of this connector. Defaults to 2048. | |
| Long value for the maximum size in bytes of the blocking queue. The feature is disabled by default, it will be active if it’s set with a positive long value. | |
| Positive integer value that specifies the number of milliseconds the connector should wait during each iteration for new change events to appear. Defaults to 1000 milliseconds, or 1 second. | |
| Positive integer value that specifies the initial delay when trying to reconnect to a primary after the first failed connection attempt or when no primary is available. Defaults to 1 second (1000 ms). | |
| Positive integer value that specifies the maximum delay when trying to reconnect to a primary after repeated failed connection attempts or when no primary is available. Defaults to 120 seconds (120,000 ms). | |
|
Positive integer value that specifies the maximum number of failed connection attempts to a replica set primary before an exception occurs and task is aborted. Defaults to 16, which with the defaults for | |
|
Boolean value that specifies whether the addresses in 'mongodb.hosts' are seeds that should be used to discover all members of the cluster or replica set ( | |
|
Controls how frequently heartbeat messages are sent.
Set this parameter to | |
|
Controls the naming of the topic to which heartbeat messages are sent. | |
| Whether field names are sanitized to adhere to Avro naming requirements. | |
comma-separated list of operation types that will be skipped during streaming. The operations include: | ||
Controls which collection items are included in snapshot. This property affects snapshots only. Specify a comma-separated list of collection names in the form databaseName.collectionName.
For each collection that you specify, also specify another configuration property: | ||
|
When set to See Transaction Metadata for additional details. | |
10000 (10 seconds) | The number of milliseconds to wait before restarting a connector after a retriable error occurs. | |
| The interval in which the connector polls for new, removed, or changed replica sets. | |
10000 (10 seconds) | The number of milliseconds the driver will wait before a new connection attempt is aborted. | |
0 |
The number of milliseconds before a send/receive on the socket can take before a timeout occurs. A value of | |
30000 (30 seconds) | The number of milliseconds the driver will wait to select a server before it times out and throws an error. | |
|
Specifies the maximum number of milliseconds the oplog cursor will wait for the server to produce a result before causing an execution timeout exception. A value of |
4.6. Monitoring Debezium MongoDB connector performance
The Debezium MongoDB connector has two metric types in addition to the built-in support for JMX metrics that Zookeeper, Kafka, and Kafka Connect have.
- Snapshot metrics provide information about connector operation while performing a snapshot.
- Streaming metrics provide information about connector operation when the connector is capturing changes and streaming change event records.
The Debezium monitoring documentation provides details about how to expose these metrics by using JMX.
4.6.1. Monitoring Debezium during MongoDB snapshots
The MBean is debezium.mongodb:type=connector-metrics,context=snapshot,server=<mongodb.server.name>
.
Snapshot metrics are not exposed unless a snapshot operation is active, or if a snapshot has occurred since the last connector start.
The following table lists the shapshot metrics that are available.
Attributes | Type | Description |
---|---|---|
| The last snapshot event that the connector has read. | |
| The number of milliseconds since the connector has read and processed the most recent event. | |
| The total number of events that this connector has seen since last started or reset. | |
| The number of events that have been filtered by include/exclude list filtering rules configured on the connector. | |
|
| The list of tables that are monitored by the connector. |
| The list of tables that are captured by the connector. | |
| The length the queue used to pass events between the snapshotter and the main Kafka Connect loop. | |
| The free capacity of the queue used to pass events between the snapshotter and the main Kafka Connect loop. | |
| The total number of tables that are being included in the snapshot. | |
| The number of tables that the snapshot has yet to copy. | |
| Whether the snapshot was started. | |
| Whether the snapshot was aborted. | |
| Whether the snapshot completed. | |
| The total number of seconds that the snapshot has taken so far, even if not complete. | |
| Map containing the number of rows scanned for each table in the snapshot. Tables are incrementally added to the Map during processing. Updates every 10,000 rows scanned and upon completing a table. | |
|
The maximum buffer of the queue in bytes. It will be enabled if | |
| The current data of records in the queue in bytes. |
The Debezium MongoDB connector also provides the following custom snapshot metrics:
Attribute | Type | Description |
---|---|---|
|
| Number of database disconnects. |
4.6.2. Monitoring Debezium MongoDB connector record streaming
The MBean is debezium.mongodb:type=connector-metrics,context=streaming,server=<mongodb.server.name>
.
The following table lists the streaming metrics that are available.
Attributes | Type | Description |
---|---|---|
| The last streaming event that the connector has read. | |
| The number of milliseconds since the connector has read and processed the most recent event. | |
| The total number of events that this connector has seen since last started or reset. | |
| The number of events that have been filtered by include/exclude list filtering rules configured on the connector. | |
|
| The list of tables that are monitored by the connector. |
| The list of tables that are captured by the connector. | |
| The length the queue used to pass events between the streamer and the main Kafka Connect loop. | |
| The free capacity of the queue used to pass events between the streamer and the main Kafka Connect loop. | |
| Flag that denotes whether the connector is currently connected to the database server. | |
| The number of milliseconds between the last change event’s timestamp and the connector processing it. The values will incoporate any differences between the clocks on the machines where the database server and the connector are running. | |
| The number of processed transactions that were committed. | |
| The coordinates of the last received event. | |
| Transaction identifier of the last processed transaction. | |
| The maximum buffer of the queue in bytes. | |
| The current data of records in the queue in bytes. |
The Debezium MongoDB connector also provides the following custom streaming metrics:
Attribute | Type | Description |
---|---|---|
|
| Number of database disconnects. |
|
| Number of primary node elections. |
4.7. How Debezium MongoDB connectors handle faults and problems
Debezium is a distributed system that captures all changes in multiple upstream databases, and will never miss or lose an event. When the system is operating normally and is managed carefully, then Debezium provides exactly once delivery of every change event.
If a fault occurs, the system does not lose any events. However, while it is recovering from the fault, it might repeat some change events. In such situations, Debezium, like Kafka, provides at least once delivery of change events.
The following topics provide details about how the Debezium MongoDB connector handles various kinds of faults and problems.
Configuration and startup errors
In the following situations, the connector fails when trying to start, reports an error or exception in the log, and stops running:
- The connector’s configuration is invalid.
- The connector cannot successfully connect to MongoDB by using the specified connection parameters.
After a failure, the connector attempts to reconnect by using exponential backoff. You can configure the maximum number of reconnection attempts.
In these cases, the error will have more details about the problem and possibly a suggested work around. The connector can be restarted when the configuration has been corrected or the MongoDB problem has been addressed.
The attempts to reconnect are controlled by three properties:
-
connect.backoff.initial.delay.ms
- The delay before attempting to reconnect for the first time, with a default of 1 second (1000 milliseconds). -
connect.backoff.max.delay.ms
- The maximum delay before attempting to reconnect, with a default of 120 seconds (120,000 milliseconds). -
connect.max.attempts
- The maximum number of attempts before an error is produced, with a default of 16.
Each delay is double that of the prior delay, up to the maximum delay. Given the default values, the following table shows the delay for each failed connection attempt and the total accumulated time before failure.
Reconnection attempt number | Delay before attempt, in seconds | Total delay before attempt, in minutes and seconds |
---|---|---|
1 | 1 | 00:01 |
2 | 2 | 00:03 |
3 | 4 | 00:07 |
4 | 8 | 00:15 |
5 | 16 | 00:31 |
6 | 32 | 01:03 |
7 | 64 | 02:07 |
8 | 120 | 04:07 |
9 | 120 | 06:07 |
10 | 120 | 08:07 |
11 | 120 | 10:07 |
12 | 120 | 12:07 |
13 | 120 | 14:07 |
14 | 120 | 16:07 |
15 | 120 | 18:07 |
16 | 120 | 20:07 |
Kafka Connect process stops gracefully
If Kafka Connect is being run in distributed mode, and a Kafka Connect process is stopped gracefully, then prior to shutdown of that processes Kafka Connect will migrate all of the process' connector tasks to another Kafka Connect process in that group, and the new connector tasks will pick up exactly where the prior tasks left off. There is a short delay in processing while the connector tasks are stopped gracefully and restarted on the new processes.
If the group contains only one process and that process is stopped gracefully, then Kafka Connect will stop the connector and record the last offset for each replica set. Upon restart, the replica set tasks will continue exactly where they left off.
Kafka Connect process crashes
If the Kafka Connector process stops unexpectedly, then any connector tasks it was running will terminate without recording their most recently-processed offsets. When Kafka Connect is being run in distributed mode, it will restart those connector tasks on other processes. However, the MongoDB connectors will resume from the last offset recorded by the earlier processes, which means that the new replacement tasks may generate some of the same change events that were processed just prior to the crash. The number of duplicate events depends on the offset flush period and the volume of data changes just before the crash.
Because there is a chance that some events may be duplicated during a recovery from failure, consumers should always anticipate some events may be duplicated. Debezium changes are idempotent, so a sequence of events always results in the same state.
Debezium also includes with each change event message the source-specific information about the origin of the event, including the MongoDB event’s unique transaction identifier (h
) and timestamp (sec
and ord
). Consumers can keep track of other of these values to know whether it has already seen a particular event.
Connector is stopped for a long interval
If the connector is gracefully stopped, the replica sets can continue to be used and any new changes are recorded in MongoDB’s oplog. When the connector is restarted, it will resume streaming changes for each replica set where it last left off, recording change events for all of the changes that were made while the connector was stopped. If the connector is stopped long enough such that MongoDB purges from its oplog some operations that the connector has not read, then upon startup the connector will perform a snapshot.
A properly configured Kafka cluster is capable of massive throughput. Kafka Connect is written with Kafka best practices, and given enough resources will also be able to handle very large numbers of database change events. Because of this, when a connector has been restarted after a while, it is very likely to catch up with the database, though how quickly will depend upon the capabilities and performance of Kafka and the volume of changes being made to the data in MongoDB.
If the connector remains stopped for long enough, MongoDB might purge older oplog files and the connector’s last position may be lost. In this case, when the connector configured with initial snapshot mode (the default) is finally restarted, the MongoDB server will no longer have the starting point and the connector will fail with an error.
MongoDB loses writes
In certain failure situations, MongoDB can lose commits, which results in the MongoDB connector being unable to capture the lost changes. For example, if the primary crashes suddenly after it applies a change and records the change to its oplog, the oplog might become unavailable before secondary nodes can read its contents. As a result, the secondary node that is elected as the new primary node might be missing the most recent changes from its oplog.
At this time, there is no way to prevent this side effect in MongoDB.
Chapter 5. Debezium connector for MySQL
This release of the Debezium MySQL connector includes a new default capturing implementation that is based on the common connector framework that is used by the other Debezium connectors. The revised capturing implementation is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service-level agreements (SLAs) and might not be functionally complete; therefore, Red Hat does not recommend implementing any Technology Preview features in production environments. This Technology Preview feature provides early access to upcoming product innovations, enabling you to test functionality and provide feedback during the development process. For more information about support scope, see Technology Preview Features Support Scope.
If the connector generates errors or unexpected behavior while running with the new capturing implementation, you can revert to the earlier implementation by setting the following configuration option:
internal.implementation=legacy
MySQL has a binary log (binlog) that records all operations in the order in which they are committed to the database. This includes changes to table schemas as well as changes to the data in tables. MySQL uses the binlog for replication and recovery.
The Debezium MySQL connector reads the binlog, produces change events for row-level INSERT
, UPDATE
, and DELETE
operations, and emits the change events to Kafka topics. Client applications read those Kafka topics.
As MySQL is typically set up to purge binlogs after a specified period of time, the MySQL connector performs an initial consistent snapshot of each of your databases. The MySQL connector reads the binlog from the point at which the snapshot was made.
For information about the MySQL Database versions that are compatible with this connector, see the Debezium Supported Configurations page.
Information and procedures for using a Debezium MySQL connector are organized as follows:
- Section 5.1, “How Debezium MySQL connectors work”
- Section 5.2, “Descriptions of Debezium MySQL connector data change events”
- Section 5.3, “How Debezium MySQL connectors map data types”
- Section 5.4, “Setting up MySQL to run a Debezium connector”
- Section 5.5, “Deployment of Debezium MySQL connectors”
- Section 5.6, “Monitoring Debezium MySQL connector performance”
- Section 5.7, “How Debezium MySQL connectors handle faults and problems”
5.1. How Debezium MySQL connectors work
An overview of the MySQL topologies that the connector supports is useful for planning your application. To optimally configure and run a Debezium MySQL connector, it is helpful to understand how the connector tracks the structure of tables, exposes schema changes, performs snapshots, and determines Kafka topic names.
Details are in the following topics:
- Section 5.1.1, “MySQL topologies supported by Debezium connectors”
- Section 5.1.2, “How Debezium MySQL connectors handle database schema changes”
- Section 5.1.3, “How Debezium MySQL connectors expose database schema changes”
- Section 5.1.4, “How Debezium MySQL connectors perform database snapshots”
- Section 5.1.5, “Default names of Kafka topics that receive Debezium MySQL change event records”
5.1.1. MySQL topologies supported by Debezium connectors
The Debezium MySQL connector supports the following MySQL topologies:
- Standalone
- When a single MySQL server is used, the server must have the binlog enabled (and optionally GTIDs enabled) so the Debezium MySQL connector can monitor the server. This is often acceptable, since the binary log can also be used as an incremental backup. In this case, the MySQL connector always connects to and follows this standalone MySQL server instance.
- Primary and replica
The Debezium MySQL connector can follow one of the primary servers or one of the replicas (if that replica has its binlog enabled), but the connector sees changes in only the cluster that is visible to that server. Generally, this is not a problem except for the multi-primary topologies.
The connector records its position in the server’s binlog, which is different on each server in the cluster. Therefore, the connector must follow just one MySQL server instance. If that server fails, that server must be restarted or recovered before the connector can continue.
- High available clusters
- A variety of high availability solutions exist for MySQL, and they make it significantly easier to tolerate and almost immediately recover from problems and failures. Most HA MySQL clusters use GTIDs so that replicas are able to keep track of all changes on any of the primary servers.
- Multi-primary
Network Database (NDB) cluster replication uses one or more MySQL replica nodes that each replicate from multiple primary servers. This is a powerful way to aggregate the replication of multiple MySQL clusters. This topology requires the use of GTIDs.
A Debezium MySQL connector can use these multi-primary MySQL replicas as sources, and can fail over to different multi-primary MySQL replicas as long as the new replica is caught up to the old replica. That is, the new replica has all transactions that were seen on the first replica. This works even if the connector is using only a subset of databases and/or tables, as the connector can be configured to include or exclude specific GTID sources when attempting to reconnect to a new multi-primary MySQL replica and find the correct position in the binlog.
- Hosted
There is support for the Debezium MySQL connector to use hosted options such as Amazon RDS and Amazon Aurora.
Because these hosted options do not allow a global read lock, table-level locks are used to create the consistent snapshot.
5.1.2. How Debezium MySQL connectors handle database schema changes
When a database client queries a database, the client uses the database’s current schema. However, the database schema can be changed at any time, which means that the connector must be able to identify what the schema was at the time each insert, update, or delete operation was recorded. Also, a connector cannot just use the current schema because the connector might be processing events that are relatively old that were recorded before the tables' schemas were changed.
To ensure correct processing of changes that occur after a schema change, MySQL includes in the binlog not only the row-level changes to the data, but also the DDL statements that are applied to the database. As the connector reads the binlog and comes across these DDL statements, it parses them and updates an in-memory representation of each table’s schema. The connector uses this schema representation to identify the structure of the tables at the time of each insert, update, or delete operation and to produce the appropriate change event. In a separate database history Kafka topic, the connector records all DDL statements along with the position in the binlog where each DDL statement appeared.
When the connector restarts after having crashed or been stopped gracefully, the connector starts reading the binlog from a specific position, that is, from a specific point in time. The connector rebuilds the table structures that existed at this point in time by reading the database history Kafka topic and parsing all DDL statements up to the point in the binlog where the connector is starting.
This database history topic is for connector use only. The connector can optionally emit schema change events to a different topic that is intended for consumer applications.
When the MySQL connector captures changes in a table to which a schema change tool such as gh-ost
or pt-online-schema-change
is applied, there are helper tables created during the migration process. The connector needs to be configured to capture change to these helper tables. If consumers do not need the records generated for helper tables, then a single message transform can be applied to filter them out.
See default names for topics that receive Debezium event records.
5.1.3. How Debezium MySQL connectors expose database schema changes
You can configure a Debezium MySQL connector to produce schema change events that describe schema changes that are applied to captured tables in the database. The connector writes schema change events to a Kafka topic named <serverName>
, where serverName
is the logical server name that is specified in the database.server.name
connector configuration property. Messages that the connector sends to the schema change topic contain a payload, and, optionally, also contain the schema of the change event message.
The payload of a schema change event message includes the following elements:
ddl
-
Provides the SQL
CREATE
,ALTER
, orDROP
statement that results in the schema change. databaseName
-
The name of the database to which the DDL statements are applied. The value of
databaseName
serves as the message key. pos
- The position in the binlog where the statements appear.
tableChanges
-
A structured representation of the entire table schema after the schema change. The
tableChanges
field contains an array that includes entries for each column of the table. Because the structured representation presents data in JSON or Avro format, consumers can easily read messages without first processing them through a DDL parser.
For a table that is in capture mode, the connector not only stores the history of schema changes in the schema change topic, but also in an internal database history topic. The internal database history topic is for connector use only and it is not intended for direct use by consuming applications. Ensure that applications that require notifications about schema changes consume that information only from the schema change topic.
Never partition the database history topic. For the database history topic to function correctly, it must maintain a consistent, global order of the event records that the connector emits to it.
To ensure that the topic is not split among partitions, set the partition count for the topic by using one of the following methods:
-
If you create the database history topic manually, specify a partition count of
1
. -
If you use the Apache Kafka broker to create the database history topic automatically, the topic is created, set the value of the Kafka
num.partitions
configuration option to1
.
The format of the messages that a connector emits to its schema change topic is in an incubating state and is subject to change without notice.
Example: Message emitted to the MySQL connector schema change topic
The following example shows a typical schema change message in JSON format. The message contains a logical representation of the table schema.
{ "schema": { ... }, "payload": { "source": { // (1) "version": "1.7.2.Final", "connector": "mysql", "name": "dbserver1", "ts_ms": 0, "snapshot": "false", "db": "inventory", "sequence": null, "table": "customers", "server_id": 0, "gtid": null, "file": "mysql-bin.000003", "pos": 219, "row": 0, "thread": null, "query": null }, "databaseName": "inventory", // (2) "schemaName": null, "ddl": "ALTER TABLE customers ADD COLUMN middle_name VARCHAR(2000)", // (3) "tableChanges": [ // (4) { "type": "ALTER", // (5) "id": "\"inventory\".\"customers\"", // (6) "table": { // (7) "defaultCharsetName": "latin1", "primaryKeyColumnNames": [ // (8) "id" ], "columns": [ // (9) { "name": "id", "jdbcType": 4, "nativeType": null, "typeName": "INT", "typeExpression": "INT", "charsetName": null, "length": 11, "scale": null, "position": 1, "optional": false, "autoIncremented": true, "generated": true }, { "name": "first_name", "jdbcType": 12, "nativeType": null, "typeName": "VARCHAR", "typeExpression": "VARCHAR", "charsetName": "latin1", "length": 255, "scale": null, "position": 2, "optional": false, "autoIncremented": false, "generated": false }, { "name": "last_name", "jdbcType": 12, "nativeType": null, "typeName": "VARCHAR", "typeExpression": "VARCHAR", "charsetName": "latin1", "length": 255, "scale": null, "position": 3, "optional": false, "autoIncremented": false, "generated": false }, { "name": "email", "jdbcType": 12, "nativeType": null, "typeName": "VARCHAR", "typeExpression": "VARCHAR", "charsetName": "latin1", "length": 255, "scale": null, "position": 4, "optional": false, "autoIncremented": false, "generated": false }, { "name": "middle_name", "jdbcType": 12, "nativeType": null, "typeName": "VARCHAR", "typeExpression": "VARCHAR", "charsetName": "latin1", "length": 2000, "scale": null, "position": 5, "optional": true, "autoIncremented": false, "generated": false } ] } } ] }, "payload": { "databaseName": "inventory", "ddl": "CREATE TABLE products ( id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY, name VARCHAR(255) NOT NULL, description VARCHAR(512), weight FLOAT ); ALTER TABLE products AUTO_INCREMENT = 101;", "source" : { "version": "1.7.2.Final", "name": "mysql-server-1", "server_id": 0, "ts_ms": 0, "gtid": null, "file": "mysql-bin.000003", "pos": 154, "row": 0, "snapshot": true, "thread": null, "db": null, "table": null, "query": null } } }
Item | Field name | Description |
---|---|---|
1 |
|
The |
2 |
|
Identifies the database and the schema that contains the change. The value of the |
3 |
|
This field contains the DDL that is responsible for the schema change. The |
4 |
| An array of one or more items that contain the schema changes generated by a DDL command. |
5 |
| Describes the kind of change. The value is one of the following:
|
6 |
|
Full identifier of the table that was created, altered, or dropped. In the case of a table rename, this identifier is a concatenation of |
7 |
| Represents table metadata after the applied change. |
8 |
| List of columns that compose the table’s primary key. |
9 |
| Metadata for each column in the changed table. |
See also: schema history topic.
5.1.4. How Debezium MySQL connectors perform database snapshots
When a Debezium MySQL connector is first started, it performs an initial consistent snapshot of your database. The following flow describes how the connector creates this snapshot. This flow is for the default snapshot mode, which is initial
. For information about other snapshot modes, see the MySQL connector snapshot.mode
configuration property.
Step | Action |
---|---|
1 |
Grabs a global read lock that blocks writes by other database clients. |
2 | Starts a transaction with repeatable read semantics to ensure that all subsequent reads within the transaction are done against the consistent snapshot. |
3 | Reads the current binlog position. |
4 | Reads the schema of the databases and tables for which the connector is configured to capture changes. |
5 | Releases the global read lock. Other database clients can now write to the database. |
6 |
If applicable, writes the DDL changes to the schema change topic, including all necessary |
7 |
Scans the database tables. For each row, the connector emits |
8 | Commits the transaction. |
9 | Records the completed snapshot in the connector offsets. |
- Connector restarts
If the connector fails, stops, or is rebalanced while performing the initial snapshot, then after the connector restarts, it performs a new snapshot. After that intial snapshot is completed, the Debezium MySQL connector restarts from the same position in the binlog so it does not miss any updates.
If the connector stops for long enough, MySQL could purge old binlog files and the connector’s position would be lost. If the position is lost, the connector reverts to the initial snapshot for its starting position. For more tips on troubleshooting the Debezium MySQL connector, see behavior when things go wrong.
- Global read locks not allowed
Some environments do not allow global read locks. If the Debezium MySQL connector detects that global read locks are not permitted, the connector uses table-level locks instead and performs a snapshot with this method. This requires the database user for the Debezium connector to have
LOCK TABLES
privileges.Table 5.3. Workflow for performing an initial snapshot with table-level locks Step Action 1
Obtains table-level locks.
2
Starts a transaction with repeatable read semantics to ensure that all subsequent reads within the transaction are done against the consistent snapshot.
3
Reads and filters the names of the databases and tables.
4
Reads the current binlog position.
5
Reads the schema of the databases and tables for which the connector is configured to capture changes.
6
If applicable, writes the DDL changes to the schema change topic, including all necessary
DROP…
andCREATE…
DDL statements.7
Scans the database tables. For each row, the connector emits
CREATE
events to the relevant table-specific Kafka topics.8
Commits the transaction.
9
Releases the table-level locks.
10
Records the completed snapshot in the connector offsets.
5.1.4.1. Ad hoc snapshots
The use of ad hoc snapshots is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service-level agreements (SLAs) and might not be functionally complete; therefore, Red Hat does not recommend implementing any Technology Preview features in production environments. This Technology Preview feature provides early access to upcoming product innovations, enabling you to test functionality and provide feedback during the development process. For more information about support scope, see Technology Preview Features Support Scope.
By default, a connector runs an initial snapshot operation only after it starts for the first time. Following this initial snapshot, under normal circumstances, the connector does not repeat the snapshot process. Any future change event data that the connector captures comes in through the streaming process only.
However, in some situations the data that the connector obtained during the initial snapshot might become stale, lost, or incomplete. To provide a mechanism for recapturing table data, Debezium includes an option to perform ad hoc snapshots. The following changes in a database might be cause for performing an ad hoc snapshot:
- The connector configuration is modified to capture a different set of tables.
- Kafka topics are deleted and must be rebuilt.
- Data corruption occurs due to a configuration error or some other problem.
You can re-run a snapshot for a table for which you previously captured a snapshot by initiating a so-called ad-hoc snapshot. Ad hoc snapshots require the use of signaling tables. You initiate an ad hoc snapshot by sending a signal request to the Debezium signaling table.
When you initiate an ad hoc snapshot of an existing table, the connector appends content to the topic that already exists for the table. If a previously existing topic was removed, Debezium can create a topic automatically if automatic topic creation is enabled.
Ad hoc snapshot signals specify the tables to include in the snapshot. The snapshot can capture the entire contents of the database, or capture only a subset of the tables in the database.
You specify the tables to capture by sending an execute-snapshot
message to the signaling table. Set the type of the execute-snapshot
signal to incremental
, and provide the names of the tables to include in the snapshot, as described in the following table:
Field | Default | Value |
---|---|---|
|
|
Specifies the type of snapshot that you want to run. |
| N/A |
An array that contains the fully-qualified names of the table to be snapshotted. |
Triggering an ad hoc snapshot
You initiate an ad hoc snapshot by adding an entry with the execute-snapshot
signal type to the signaling table. After the connector processes the message, it begins the snapshot operation. The snapshot process reads the first and last primary key values and uses those values as the start and end point for each table. Based on the number of entries in the table, and the configured chunk size, Debezium divides the table into chunks, and proceeds to snapshot each chunk, in succession, one at a time.
Currently, the execute-snapshot
action type triggers incremental snapshots only. For more information, see Incremental snapshots.
5.1.4.2. Incremental snapshots
The use of incremental snapshots is a Technology Preview feature. Technology Preview features are not supported with Red Hat production service-level agreements (SLAs) and might not be functionally complete; therefore, Red Hat does not recommend implementing any Technology Preview features in production environments. This Technology Preview feature provides early access to upcoming product innovations, enabling you to test functionality and provide feedback during the development process. For more information about support scope, see Technology Preview Features Support Scope.
To provide flexibility in managing snapshots, Debezium includes a supplementary snapshot mechanism, known as incremental snapshotting. Incremental snapshots rely on the Debezium mechanism for sending signals to a Debezium connector.
In an incremental snapshot, instead of capturing the full state of a database all at once, as in an initial snapshot, Debezium captures each table in phases, in a series of configurable chunks. You can specify the tables that you want the snapshot to capture and the size of each chunk. The chunk size determines the number of rows that the snapshot collects during each fetch operation on the database. The default chunk size for incremental snapshots is 1 KB.
As an incremental snapshot proceeds, Debezium uses watermarks to track its progress, maintaining a record of each table row that it captures. This phased approach to capturing data provides the following advantages over the standard initial snapshot process:
- You can run incremental snapshots in parallel with streamed data capture, instead of postponing streaming until the snapshot completes. The connector continues to capture near real-time events from the change log throughout the snapshot process, and neither operation blocks the other.
- If the progress of an incremental snapshot is interrupted, you can resume it without losing any data. After the process resumes, the snapshot begins at the point where it stopped, rather than recapturing the table from the beginning.
-
You can run an incremental snapshot on demand at any time, and repeat the process as needed to adapt to database updates. For example, you might re-run a snapshot after you modify the connector configuration to add a table to its
table.include.list
property.
Incremental snapshot process
When you run an incremental snapshot, Debezium sorts each table by primary key and then splits the table into chunks based on the configured chunk size. Working chunk by chunk, it then captures each table row in a chunk. For each row that it captures, the snapshot emits a READ
event. That event represents the value of the row when the snapshot for the chunk began.
As a snapshot proceeds, it’s likely that other processes continue to access the database, potentially modifying table records. To reflect such changes, INSERT
, UPDATE
, or DELETE
operations are committed to the transaction log as per usual. Similarly, the ongoing Debezium streaming process continues to detect these change events and emits corresponding change event records to Kafka.
How Debezium resolves collisions among records with the same primary key
In some cases, the UPDATE
or DELETE
events that the streaming process emits are received out of sequence. That is, the streaming process might emit an event that modifies a table row before the snapshot captures the chunk that contains the READ
event for that row. When the snapshot eventually emits the corresponding READ
event for the row, its value is already superseded. To ensure that incremental snapshot events that arrive out of sequence are processed in the correct logical order, Debezium employs a buffering scheme for resolving collisions. Only after collisions between the snapshot events and the streamed events are resolved does Debezium emit an event record to Kafka.
Snapshot window
To assist in resolving collisions between late-arriving READ
events and streamed events that modify the same table row, Debezium employs a so-called snapshot window. The snapshot windows demarcates the interval during which an incremental snapshot captures data for a specified table chunk. Before the snapshot window for a chunk opens, Debezium follows its usual behavior and emits events from the transaction log directly downstream to the target Kafka topic. But from the moment that the snapshot for a particular chunk opens, until it closes, Debezium performs a de-duplication step to resolve collisions between events that have the same primary key..
For each data collection, the Debezium emits two types of events, and stores the records for them both in a single destination Kafka topic. The snapshot records that it captures directly from a table are emitted as READ
operations. Meanwhile, as users continue to update records in the data collection, and the transaction log is updated to reflect each commit, Debezium emits UPDATE
or DELETE
operations for each change.
As the snapshot window opens, and Debezium begins processing a snapshot chunk, it delivers snapshot records to a memory buffer. During the snapshot windows, the primary keys of the READ
events in the buffer are compared to the primary keys of the incoming streamed events. If no match is found, the streamed event record is sent directly to Kafka. If Debezium detects a match, it discards the buffered READ
event, and writes the streamed record to the destination topic, because the streamed event logically supersede the static snapshot event. After the snapshot window for the chunk closes, the buffer contains only READ
events for which no related transaction log events exist. Debezium emits these remaining READ
events to the table’s Kafka topic.
The connector repeats the process for each snapshot chunk.
Triggering an incremental snapshot
Currently, the only way to initiate an incremental snapshot is to send an ad hoc snapshot signal to the signaling table on the source database. You submit signals to the table as SQL INSERT
queries. After Debezium detects the change in the signaling table, it reads the signal, and runs the requested snapshot operation.
The query that you submit specifies the tables to include in the snapshot, and, optionally, specifies the kind of snapshot operation. Currently, the only valid option for snapshots operations is the default value, incremental
.
To specify the tables to include in the snapshot, provide a data-collections
array that lists the tables, for example,{"data-collections": ["public.MyFirstTable", "public.MySecondTable"]}
The data-collections
array for an incremental snapshot signal has no default value. If the data-collections
array is empty, Debezium detects that no action is required and does not perform a snapshot.
Prerequisites
- A signaling data collection exists on the source database and the connector is configured to capture it.
-
The signaling data collection is specified in the
signal.data.collection
property.
Procedure
Send a SQL query to add the ad hoc incremental snapshot request to the signaling table:
INSERT INTO _<signalTable>_ (id, type, data) VALUES (_'<id>'_, _'<snapshotType>'_, '{"data-collections": ["_<tableName>_","_<tableName>_"],"type":"_<snapshotType>_"}');
For example,
INSERT INTO myschema.debezium_signal (id, type, data) VALUES('ad-hoc-1', 'execute-snapshot', '{"data-collections": ["schema1.table1", "schema2.table2"],"type":"incremental"}');
The values of the
id
,type
, anddata
parameters in the command correspond to the fields of the signaling table.The following table describes the these parameters:
Table 5.5. Descriptions of fields in a SQL command for sending an incremental snapshot signal to the signaling table Value Description myschema.debezium_signal
Specifies the fully-qualified name of the signaling table on the source database
ad-hoc-1
The
id
parameter specifies an arbitrary string that is assigned as theid
identifier for the signal request.
Use this string to identify logging messages to entries in the signaling table. Debezium does not use this string. Rather, during the snapshot, Debezium generates its ownid
string as a watermarking signal.execute-snapshot
Specifies
type
parameter specifies the operation that the signal is intended to trigger.
data-collections
A required component of the
data
field of a signal that specifies an array of table names to include in the snapshot.
The array lists tables by their fully-qualified names, using the same format as you use to specify the name of the connector’s signaling table in thesignal.data.collection
configuration property.incremental
An optional
type
component of thedata
field of a signal that specifies the kind of snapshot operation to run.
Currently, the only valid option is the default value,incremental
.
Specifying atype
value in the SQL query that you submit to the signaling table is optional.
If you do not specify a value, the connector runs an incremental snapshot.
The following example, shows the JSON for an incremental snapshot event that is captured by a connector.
Example: Incremental snapshot event message
{ "before":null, "after": { "pk":"1", "value":"New data" }, "source": { ... "snapshot":"incremental" 1 }, "op":"r", 2 "ts_ms":"1620393591654", "transaction":null }
Item | Field name | Description |
---|---|---|
1 |
|
Specifies the type of snapshot operation to run. |
2 |
|
Specifies the event type. |
5.1.5. Default names of Kafka topics that receive Debezium MySQL change event records
By default, the MySQL connector writes change events for all of the INSERT
, UPDATE
, and DELETE
operations that occur in a table to a single Apache Kafka topic that is specific to that table.
The connector uses the following convention to name change event topics:
serverName.databaseName.tableName
Suppose that fulfillment
is the server name, inventory
is the database name, and the database contains tables named orders
, customers
, and products
. The Debezium MySQL connector emits events to three Kafka topics, one for each table in the database:
fulfillment.inventory.orders fulfillment.inventory.customers fulfillment.inventory.products
The following list provides definitions for the components of the default name:
- serverName
-
The logical name of the server as specified by the
database.server.name
connector configuration property. - schemaName
- The name of the schema in which the operation occurred.
- tableName
- The name of the table in which the operation occurred.
The connector applies similar naming conventions to label its internal database history topics, schema change topics, and transaction metadata topics.
If the default topic name do not meet your requirements, you can configure custom topic names. To configure custom topic names, you specify regular expressions in the logical topic routing SMT. For more information about using the logical topic routing SMT to customize topic naming, see Topic routing.
Transaction metadata
Debezium can generate events that represent transaction boundaries and that enrich data change event messages.
Debezium registers and receives metadata only for transactions that occur after you deploy the connector. Metadata for transactions that occur before you deploy the connector is not available.
Debezium generates transaction boundary events for the BEGIN
and END
delimiters in every transaction. Transaction boundary events contain the following fields:
status
-
BEGIN
orEND
. id
- String representation of the unique transaction identifier.
event_count
(forEND
events)- Total number of events emitted by the transaction.
data_collections
(forEND
events)-
An array of pairs of
data_collection
andevent_count
elements. that indicates the number of events that the connector emits for changes that originate from a data collection.
Example
{ "status": "BEGIN", "id": "0e4d5dcd-a33b-11ea-80f1-02010a22a99e:10", "event_count": null, "data_collections": null } { "status": "END", "id": "0e4d5dcd-a33b-11ea-80f1-02010a22a99e:10", "event_count": 2, "data_collections": [ { "data_collection": "s1.a", "event_count": 1 }, { "data_collection": "s2.a", "event_count": 1 } ] }
The connector emits transaction events to the <database.server.name>
.transaction
topic.
Change data event enrichment
When transaction metadata is enabled the data message Envelope
is enriched with a new transaction
field. This field provides information about every event in the form of a composite of fields:
-
id
- string representation of unique transaction identifier -
total_order
- absolute position of the event among all events generated by the transaction -
data_collection_order
- the per-data collection position of the event among all events that were emitted by the transaction
Following is an example of a message:
{ "before": null, "after": { "pk": "2", "aa": "1" }, "source": { ... }, "op": "c", "ts_ms": "1580390884335", "transaction": { "id": "0e4d5dcd-a33b-11ea-80f1-02010a22a99e:10", "total_order": "1", "data_collection_order": "1" } }
For systems which don’t have GTID enabled, the transaction identifier is constructed using the combination of binlog filename and binlog position. For example, if the binlog filename and position corresponding to the transaction BEGIN event are mysql-bin.000002 and 1913 respectively then the Debezium constructed transaction identifier would be file=mysql-bin.000002,pos=1913
.
5.2. Descriptions of Debezium MySQL connector data change events
The Debezium MySQL connector generates a data change event for each row-level INSERT
, UPDATE
, and DELETE
operation. Each event contains a key and a value. The structure of the key and the value depends on the table that was changed.
Debezium and Kafka Connect are designed around continuous streams of event messages. However, the structure of these events may change over time, which can be difficult for consumers to handle. To address this, each event contains the schema for its content or, if you are using a schema registry, a schema ID that a consumer can use to obtain the schema from the registry. This makes each event self-contained.
The following skeleton JSON shows the basic four parts of a change event. However, how you configure the Kafka Connect converter that you choose to use in your application determines the representation of these four parts in change events. A schema
field is in a change event only when you configure the converter to produce it. Likewise, the event key and event payload are in a change event only if you configure a converter to produce it. If you use the JSON converter and you configure it to produce all four basic change event parts, change events have this structure:
{ "schema": { 1 ... }, "payload": { 2 ... }, "schema": { 3 ... }, "payload": { 4 ... }, }
Item | Field name | Description |
---|---|---|
1 |
|
The first |
2 |
|
The first |
3 |
|
The second |
4 |
|
The second |
By default, the connector streams change event records to topics with names that are the same as the event’s originating table. See topic names.
The MySQL connector ensures that all Kafka Connect schema names adhere to the Avro schema name format. This means that the logical server name must start with a Latin letter or an underscore, that is, a-z, A-Z, or _. Each remaining character in the logical server name and each character in the database and table names must be a Latin letter, a digit, or an underscore, that is, a-z, A-Z, 0-9, or _. If there is an invalid character it is replaced with an underscore character.
This can lead to unexpected conflicts if the logical server name, a database name, or a table name contains invalid characters, and the only characters that distinguish names from one another are invalid and thus replaced with underscores.
More details are in the following topics:
5.2.1. About keys in Debezium MySQL change events
A change event’s key contains the schema for the changed table’s key and the changed row’s actual key. Both the schema and its corresponding payload contain a field for each column in the changed table’s PRIMARY KEY
(or unique constraint) at the time the connector created the event.
Consider the following customers
table, which is followed by an example of a change event key for this table.
CREATE TABLE customers ( id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR(255) NOT NULL, last_name VARCHAR(255) NOT NULL, email VARCHAR(255) NOT NULL UNIQUE KEY ) AUTO_INCREMENT=1001;
Every change event that captures a change to the customers
table has the same event key schema. For as long as the customers
table has the previous definition, every change event that captures a change to the customers
table has the following key structure. In JSON, it looks like this:
{ "schema": { 1 "type": "struct", "name": "mysql-server-1.inventory.customers.Key", 2 "optional": false, 3 "fields": [ 4 { "field": "id", "type": "int32", "optional": false } ] }, "payload": { 5 "id": 1001 } }
Item | Field name | Description |
---|---|---|
1 |
|
The schema portion of the key specifies a Kafka Connect schema that describes what is in the key’s |
2 |
|
Name of the schema that defines the structure of the key’s payload. This schema describes the structure of the primary key for the table that was changed. Key schema names have the format connector-name.database-name.table-name.
|
3 |
|
Indicates whether the event key must contain a value in its |
4 |
|
Specifies each field that is expected in the |
5 |
|
Contains the key for the row for which this change event was generated. In this example, the key, contains a single |
5.2.2. About values in Debezium MySQL change events
The value in a change event is a bit more complicated than the key. Like the key, the value has a schema
section and a payload
section. The schema
section contains the schema that describes the Envelope
structure of the payload
section, including its nested fields. Change events for operations that create, update or delete data all have a value payload with an envelope structure.
Consider the same sample table that was used to show an example of a change event key:
CREATE TABLE customers ( id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR(255) NOT NULL, last_name VARCHAR(255) NOT NULL, email VARCHAR(255) NOT NULL UNIQUE KEY ) AUTO_INCREMENT=1001;
The value portion of a change event for a change to this table is described for:
create events
The following example shows the value portion of a change event that the connector generates for an operation that creates data in the customers
table:
{ "schema": { 1 "type": "struct", "fields": [ { "type": "struct", "fields": [ { "type": "int32", "optional": false, "field": "id" }, { "type": "string", "optional": false, "field": "first_name" }, { "type": "string", "optional": false, "field": "last_name" }, { "type": "string", "optional": false, "field": "email" } ], "optional": true, "name": "mysql-server-1.inventory.customers.Value", 2 "field": "before" }, { "type": "struct", "fields": [ { "type": "int32", "optional": false, "field": "id" }, { "type": "string", "optional": false, "field": "first_name" }, { "type": "string", "optional": false, "field": "last_name" }, { "type": "string", "optional": false, "field": "email" } ], "optional": true, "name": "mysql-server-1.inventory.customers.Value", "field": "after" }, { "type": "struct", "fields": [ { "type": "string", "optional": false, "field": "version" }, { "type": "string", "optional": false, "field": "connector" }, { "type": "string", "optional": false, "field": "name" }, { "type": "int64", "optional": false, "field": "ts_ms" }, { "type": "boolean", "optional": true, "default": false, "field": "snapshot" }, { "type": "string", "optional": false, "field": "db" }, { "type": "string", "optional": true, "field": "table" }, { "type": "int64", "optional": false, "field": "server_id" }, { "type": "string", "optional": true, "field": "gtid" }, { "type": "string", "optional": false, "field": "file" }, { "type": "int64", "optional": false, "field": "pos" }, { "type": "int32", "optional": false, "field": "row" }, { "type": "int64", "optional": true, "field": "thread" }, { "type": "string", "optional": true, "field": "query" } ], "optional": false, "name": "io.debezium.connector.mysql.Source", 3 "field": "source" }, { "type": "string", "optional": false, "field": "op" }, { "type": "int64", "optional": true, "field": "ts_ms" } ], "optional": false, "name": "mysql-server-1.inventory.customers.Envelope" 4 }, "payload": { 5 "op": "c", 6 "ts_ms": 1465491411815, 7 "before": null, 8 "after": { 9 "id": 1004, "first_name": "Anne", "last_name": "Kretchmar", "email": "annek@noanswer.org" }, "source": { 10 "version": "1.7.2.Final", "connector": "mysql", "name": "mysql-server-1", "ts_ms": 0, "snapshot": false, "db": "inventory", "table": "customers", "server_id": 0, "gtid": null, "file": "mysql-bin.000003", "pos": 154, "row": 0, "thread": 7, "query": "INSERT INTO customers (first_name, last_name, email) VALUES ('Anne', 'Kretchmar', 'annek@noanswer.org')" } } }
Item | Field name | Description |
---|---|---|
1 |
| The value’s schema, which describes the structure of the value’s payload. A change event’s value schema is the same in every change event that the connector generates for a particular table. |
2 |
|
In the |
3 |
|
|
4 |
|
|
5 |
|
The value’s actual data. This is the information that the change event is providing. |
6 |
|
Mandatory string that describes the type of operation that caused the connector to generate the event. In this example,
|
7 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
8 |
|
An optional field that specifies the state of the row before the event occurred. When the |
9 |
|
An optional field that specifies the state of the row after the event occurred. In this example, the |
10 |
| Mandatory field that describes the source metadata for the event. This field contains information that you can use to compare this event with other events, with regard to the origin of the events, the order in which the events occurred, and whether events were part of the same transaction. The source metadata includes:
If the |
update events
The value of a change event for an update in the sample customers
table has the same schema as a create event for that table. Likewise, the event value’s payload has the same structure. However, the event value payload contains different values in an update event. Here is an example of a change event value in an event that the connector generates for an update in the customers
table:
{ "schema": { ... }, "payload": { "before": { 1 "id": 1004, "first_name": "Anne", "last_name": "Kretchmar", "email": "annek@noanswer.org" }, "after": { 2 "id": 1004, "first_name": "Anne Marie", "last_name": "Kretchmar", "email": "annek@noanswer.org" }, "source": { 3 "version": "1.7.2.Final", "name": "mysql-server-1", "connector": "mysql", "name": "mysql-server-1", "ts_ms": 1465581029100, "snapshot": false, "db": "inventory", "table": "customers", "server_id": 223344, "gtid": null, "file": "mysql-bin.000003", "pos": 484, "row": 0, "thread": 7, "query": "UPDATE customers SET first_name='Anne Marie' WHERE id=1004" }, "op": "u", 4 "ts_ms": 1465581029523 5 } }
Item | Field name | Description |
---|---|---|
1 |
|
An optional field that specifies the state of the row before the event occurred. In an update event value, the |
2 |
|
An optional field that specifies the state of the row after the event occurred. You can compare the |
3 |
|
Mandatory field that describes the source metadata for the event. The
If the |
4 |
|
Mandatory string that describes the type of operation. In an update event value, the |
5 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
Updating the columns for a row’s primary/unique key changes the value of the row’s key. When a key changes, Debezium outputs three events: a DELETE
event and a tombstone event with the old key for the row, followed by an event with the new key for the row. Details are in the next section.
Primary key updates
An UPDATE
operation that changes a row’s primary key field(s) is known as a primary key change. For a primary key change, in place of an UPDATE
event record, the connector emits a DELETE
event record for the old key and a CREATE
event record for the new (updated) key. These events have the usual structure and content, and in addition, each one has a message header related to the primary key change:
-
The
DELETE
event record has__debezium.newkey
as a message header. The value of this header is the new primary key for the updated row. -
The
CREATE
event record has__debezium.oldkey
as a message header. The value of this header is the previous (old) primary key that the updated row had.
delete events
The value in a delete change event has the same schema
portion as create and update events for the same table. The payload
portion in a delete event for the sample customers
table looks like this:
{ "schema": { ... }, "payload": { "before": { 1 "id": 1004, "first_name": "Anne Marie", "last_name": "Kretchmar", "email": "annek@noanswer.org" }, "after": null, 2 "source": { 3 "version": "1.7.2.Final", "connector": "mysql", "name": "mysql-server-1", "ts_ms": 1465581902300, "snapshot": false, "db": "inventory", "table": "customers", "server_id": 223344, "gtid": null, "file": "mysql-bin.000003", "pos": 805, "row": 0, "thread": 7, "query": "DELETE FROM customers WHERE id=1004" }, "op": "d", 4 "ts_ms": 1465581902461 5 } }
Item | Field name | Description |
---|---|---|
1 |
|
Optional field that specifies the state of the row before the event occurred. In a delete event value, the |
2 |
|
Optional field that specifies the state of the row after the event occurred. In a delete event value, the |
3 |
|
Mandatory field that describes the source metadata for the event. In a delete event value, the
If the |
4 |
|
Mandatory string that describes the type of operation. The |
5 |
|
Optional field that displays the time at which the connector processed the event. The time is based on the system clock in the JVM running the Kafka Connect task. |
A delete change event record provides a consumer with the information it needs to process the removal of this row. The old values are included because some consumers might require them in order to properly handle the removal.
MySQL connector events are designed to work with Kafka log compaction. Log compaction enables removal of some older messages as long as at least the most recent message for every key is kept. This lets Kafka reclaim storage space while ensuring that the topic contains a complete data set and can be used for reloading key-based state.
Tombstone events
When a row is deleted, the delete event value still works with log compaction, because Kafka can remove all earlier messages that have that same key. However, for Kafka to remove all messages that have that same key, the message value must be null
. To make this possible, after Debezium’s MySQL connector emits a delete event, the connector emits a special tombstone event that has the same key but a null
value.
5.3. How Debezium MySQL connectors map data types
The Debezium MySQL connector represents changes to rows with events that are structured like the table in which the row exists. The event contains a field for each column value. The MySQL data type of that column dictates how Debezium represents the value in the event.
Columns that store strings are defined in MySQL with a character set and collation. The MySQL connector uses the column’s character set when reading the binary representation of the column values in the binlog events.
The connector can map MySQL data types to both literal and semantic types.
- Literal type: how the value is represented using Kafka Connect schema types
- Semantic type: how the Kafka Connect schema captures the meaning of the field (schema name)
Details are in the following sections:
Basic types
The following table shows how the connector maps basic MySQL data types.
MySQL type | Literal type | Semantic type |
---|---|---|
|
| n/a |
|
| n/a |
|
|
|
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
| n/a |
|
|
n/a |
|
|
n/a |
|
|
n/a |
|
| n/a |
|
|
n/a |
|
| n/a |
|
|
n/a |
|
| n/a |
|
|
n/a |
|
| n/a |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Temporal types
Excluding the TIMESTAMP
data type, MySQL temporal types depend on the value of the time.precision.mode
connector configuration property. For TIMESTAMP
columns whose default value is specified as CURRENT_TIMESTAMP
or NOW
, the value 1970-01-01 00:00:00
is used as the default value in the Kafka Connect schema.
MySQL allows zero-values for DATE
, DATETIME
, and TIMESTAMP
columns because zero-values are sometimes preferred over null values. The MySQL connector represents zero-values as null values when the column definition allows null values, or as the epoch day when the column does not allow null values.
Temporal values without time zones
The DATETIME
type represents a local date and time such as "2018-01-13 09:48:27". As you can see, there is no time zone information. Such columns are converted into epoch milliseconds or microseconds based on the column’s precision by using UTC. The TIMESTAMP
type represents a timestamp without time zone information. It is converted by MySQL from the server (or session’s) current time zone into UTC when writing and from UTC into the server (or session’s) current time zone when reading back the value. For example:
-
DATETIME
with a value of2018-06-20 06:37:03
becomes1529476623000
. -
TIMESTAMP
with a value of2018-06-20 06:37:03
becomes2018-06-20T13:37:03Z
.
Such columns are converted into an equivalent io.debezium.time.ZonedTimestamp
in UTC based on the server (or session’s) current time zone. The time zone will be queried from the server by default. If this fails, it must be specified explicitly by the database connectionTimeZone
MySQL configuration option. For example, if the database’s time zone (either globally or configured for the connector by means of the connectionTimeZone
option) is "America/Los_Angeles", the TIMESTAMP value "2018-06-20 06:37:03" is represented by a ZonedTimestamp
with the value "2018-06-20T13:37:03Z".
The time zone of the JVM running Kafka Connect and Debezium does not affect these conversions.
More details about properties related to temporal values are in the documentation for MySQL connector configuration properties.
- time.precision.mode=adaptive_time_microseconds(default)
The MySQL connector determines the literal type and semantic type based on the column’s data type definition so that events represent exactly the values in the database. All time fields are in microseconds. Only positive
TIME
field values in the range of00:00:00.000000
to23:59:59.999999
can be captured correctly.Table 5.12. Mappings when time.precision.mode=adaptive_time_microseconds MySQL type Literal type Semantic type DATE
INT32
io.debezium.time.Date
Represents the number of days since the epoch.TIME[(M)]
INT64
io.debezium.time.MicroTime
Represents the time value in microseconds and does not include time zone information. MySQL allowsM
to be in the range of0-6
.DATETIME, DATETIME(0), DATETIME(1), DATETIME(2), DATETIME(3)
INT64
io.debezium.time.Timestamp
Represents the number of milliseconds past the epoch and does not include time zone information.DATETIME(4), DATETIME(5), DATETIME(6)
INT64
io.debezium.time.MicroTimestamp
Represents the number of microseconds past the epoch and does not include time zone information.- time.precision.mode=connect
The MySQL connector uses defined Kafka Connect logical types. This approach is less precise than the default approach and the events could be less precise if the database column has a fractional second precision value of greater than
3
. Values in only the range of00:00:00.000
to23:59:59.999
can be handled. Settime.precision.mode=connect
only if you can ensure that theTIME
values in your tables never exceed the supported ranges. Theconnect
setting is expected to be removed in a future version of Debezium.Table 5.13. Mappings when time.precision.mode=connect MySQL type Literal type Semantic type DATE
INT32
org.apache.kafka.connect.data.Date
Represents the number of days since the epoch.TIME[(M)]
INT64
org.apache.kafka.connect.data.Time
Represents the time value in microseconds since midnight and does not include time zone information.DATETIME[(M)]
INT64
org.apache.kafka.connect.data.Timestamp
Represents the number of milliseconds since the epoch, and does not include time zone information.
Decimal types
Debezium connectors handle decimals according to the setting of the decimal.handling.mode
connector configuration property.
- decimal.handling.mode=precise
Table 5.14. Mappings when decimal.handing.mode=precise MySQL type Literal type Semantic type NUMERIC[(M[,D])]
BYTES
org.apache.kafka.connect.data.Decimal
Thescale
schema parameter contains an integer that represents how many digits the decimal point shifted.DECIMAL[(M[,D])]
BYTES
org.apache.kafka.connect.data.Decimal
Thescale
schema parameter contains an integer that represents how many digits the decimal point shifted.- decimal.handling.mode=double
Table 5.15. Mappings when decimal.handing.mode=double MySQL type Literal type Semantic type NUMERIC[(M[,D])]
FLOAT64
n/a
DECIMAL[(M[,D])]
FLOAT64
n/a
- decimal.handling.mode=string
Table 5.16. Mappings when decimal.handing.mode=string MySQL type Literal type Semantic type NUMERIC[(M[,D])]
STRING
n/a
DECIMAL[(M[,D])]
STRING
n/a
Boolean values
MySQL handles the BOOLEAN
value internally in a specific way. The BOOLEAN
column is internally mapped to the TINYINT(1)
data type. When the table is created during streaming then it uses proper BOOLEAN
mapping as Debezium receives the original DDL. During snapshots, Debezium executes SHOW CREATE TABLE
to obtain table definitions that return TINYINT(1)
for both BOOLEAN
and TINYINT(1)
columns. Debezium then has no way to obtain the original type mapping and so maps to TINYINT(1)
.
Following is an example configuration:
converters=boolean boolean.type=io.debezium.connector.mysql.converters.TinyIntOneToBooleanConverter boolean.selector=db1.table1.*, db1.table2.column1
Spatial types
Currently, the Debezium MySQL connector supports the following spatial data types.
MySQL type | Literal type | Semantic type |
---|---|---|
|
|
|
5.4. Setting up MySQL to run a Debezium connector
Some MySQL setup tasks are required before you can install and run a Debezium connector.
Details are in the following sections:
- Section 5.4.1, “Creating a MySQL user for a Debezium connector”
- Section 5.4.2, “Enabling the MySQL binlog for Debezium”
- Section 5.4.3, “Enabling MySQL Global Transaction Identifiers for Debezium”
- Section 5.4.4, “Configuring MySQL session timesouts for Debezium”
- Section 5.4.5, “Enabling query log events for Debezium MySQL connectors”
5.4.1. Creating a MySQL user for a Debezium connector
A Debezium MySQL connector requires a MySQL user account. This MySQL user must have appropriate permissions on all databases for which the Debezium MySQL connector captures changes.
Prerequisites
- A MySQL server.
- Basic knowledge of SQL commands.
Procedure
Create the MySQL user:
mysql> CREATE USER 'user'@'localhost' IDENTIFIED BY 'password';
Grant the required permissions to the user:
mysql> GRANT SELECT, RELOAD, SHOW DATABASES, REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'user' IDENTIFIED BY 'password';
The table below describes the permissions.
ImportantIf using a hosted option such as Amazon RDS or Amazon Aurora that does not allow a global read lock, table-level locks are used to create the consistent snapshot. In this case, you need to also grant
LOCK TABLES
permissions to the user that you create. See snapshots for more details.Finalize the user’s permissions:
mysql> FLUSH PRIVILEGES;
Keyword | Description |
---|---|
| Enables the connector to select rows from tables in databases. This is used only when performing a snapshot. |
|
Enables the connector the use of the |
|
Enables the connector to see database names by issuing the |
| Enables the connector to connect to and read the MySQL server binlog. |
| Enables the connector the use of the following statements:
The connector always requires this. |
| Identifies the database to which the permissions apply. |
| Specifies the user to grant the permissions to. |
| Specifies the user’s MySQL password. |
5.4.2. Enabling the MySQL binlog for Debezium
You must enable binary logging for MySQL replication. The binary logs record transaction updates for replication tools to propagate changes.
Prerequisites
- A MySQL server.
- Appropriate MySQL user privileges.
Procedure
Check whether the
log-bin
option is already on:mysql> SELECT variable_value as "BINARY LOGGING STATUS (log-bin) ::" FROM information_schema.global_variables WHERE variable_name='log_bin';
If it is
OFF
, configure your MySQL server configuration file with the following properties, which are described in the table below:server-id = 223344 log_bin = mysql-bin binlog_format = ROW binlog_row_image = FULL expire_logs_days = 10
Confirm your changes by checking the binlog status once more:
mysql> SELECT variable_value as "BINARY LOGGING STATUS (log-bin) ::" FROM information_schema.global_variables WHERE variable_name='log_bin';
Property | Description |
---|---|
|
The value for the |
|
The value of |
|
The |
|
The |
|
This is the number of days for automatic binlog file removal. The default is |
5.4.3. Enabling MySQL Global Transaction Identifiers for Debezium
Global transaction identifiers (GTIDs) uniquely identify transactions that occur on a server within a cluster. Though not required for a Debezium MySQL connector, using GTIDs simplifies replication and enables you to more easily confirm if primary and replica servers are consistent.
GTIDs are available in MySQL 5.6.5 and later. See the MySQL documentation for more details.
Prerequisites
- A MySQL server.
- Basic knowledge of SQL commands.
- Access to the MySQL configuration file.
Procedure
Enable
gtid_mode
:mysql> gtid_mode=ON
Enable
enforce_gtid_consistency
:mysql> enforce_gtid_consistency=ON
Confirm the changes:
mysql> show global variables like '%