Chapter 15. Cassandra CQL
Both producer and consumer are supported
Apache Cassandra is an open source NoSQL database designed to handle large amounts on commodity hardware. Like Amazon’s DynamoDB, Cassandra has a peer-to-peer and master-less architecture to avoid single point of failure and garanty high availability. Like Google’s BigTable, Cassandra data is structured using column families which can be accessed through the Thrift RPC API or a SQL-like API called CQL.
This component aims at integrating Cassandra 2.0+ using the CQL3 API (not the Thrift API). It’s based on Cassandra Java Driver provided by DataStax.
15.1. Configuring Options
Camel components are configured on two separate levels:
- component level
- endpoint level
15.1.1. Configuring Component Options
The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.
Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.
Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.
15.1.2. Configuring Endpoint Options
Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.
Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL as a type safe way of configuring endpoints.
A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.
The following two sections lists all the options, firstly for the component followed by the endpoint.
15.2. Component Options
The Cassandra CQL component supports 3 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
bridgeErrorHandler (consumer) | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | boolean |
lazyStartProducer (producer) | Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. | false | boolean |
autowiredEnabled (advanced) | Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. | true | boolean |
15.3. Endpoint Options
The Cassandra CQL endpoint is configured using URI syntax:
cql:beanRef:hosts:port/keyspace
with the following path and query parameters:
15.3.1. Path Parameters (4 parameters)
Name | Description | Default | Type |
---|---|---|---|
beanRef (common) | beanRef is defined using bean:id. | String | |
hosts (common) | Hostname(s) Cassandra server(s). Multiple hosts can be separated by comma. | String | |
port (common) | Port number of Cassandra server(s). | Integer | |
keyspace (common) | Keyspace to use. | String |
15.3.2. Query Parameters (30 parameters)
Name | Description | Default | Type |
---|---|---|---|
clusterName (common) | Cluster name. | String | |
consistencyLevel (common) | Consistency level to use. Enum values:
| DefaultConsistencyLevel | |
cql (common) | CQL query to perform. Can be overridden with the message header with key CamelCqlQuery. | String | |
datacenter (common) | Datacenter to use. | datacenter1 | String |
loadBalancingPolicyClass (common) | To use a specific LoadBalancingPolicyClass. | String | |
password (common) | Password for session authentication. | String | |
prepareStatements (common) | Whether to use PreparedStatements or regular Statements. | true | boolean |
resultSetConversionStrategy (common) | To use a custom class that implements logic for converting ResultSet into message body ALL, ONE, LIMIT_10, LIMIT_100… | ResultSetConversionStrategy | |
session (common) | To use the Session instance (you would normally not use this option). | CqlSession | |
username (common) | Username for session authentication. | String | |
bridgeErrorHandler (consumer) | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | boolean |
sendEmptyMessageWhenIdle (consumer) | If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead. | false | boolean |
exceptionHandler (consumer (advanced)) | To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. | ExceptionHandler | |
exchangePattern (consumer (advanced)) | Sets the exchange pattern when the consumer creates an exchange. Enum values:
| ExchangePattern | |
pollStrategy (consumer (advanced)) | A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel. | PollingConsumerPollStrategy | |
lazyStartProducer (producer) | Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. | false | boolean |
backoffErrorThreshold (scheduler) | The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in. | int | |
backoffIdleThreshold (scheduler) | The number of subsequent idle polls that should happen before the backoffMultipler should kick-in. | int | |
backoffMultiplier (scheduler) | To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured. | int | |
delay (scheduler) | Milliseconds before the next poll. | 500 | long |
greedy (scheduler) | If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the previous run polled 1 or more messages. | false | boolean |
initialDelay (scheduler) | Milliseconds before the first poll starts. | 1000 | long |
repeatCount (scheduler) | Specifies a maximum limit of number of fires. So if you set it to 1, the scheduler will only fire once. If you set it to 5, it will only fire five times. A value of zero or negative means fire forever. | 0 | long |
runLoggingLevel (scheduler) | The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that. Enum values:
| TRACE | LoggingLevel |
scheduledExecutorService (scheduler) | Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool. | ScheduledExecutorService | |
scheduler (scheduler) | To use a cron scheduler from either camel-spring or camel-quartz component. Use value spring or quartz for built in scheduler. | none | Object |
schedulerProperties (scheduler) | To configure additional properties when using a custom scheduler or any of the Quartz, Spring based scheduler. | Map | |
startScheduler (scheduler) | Whether the scheduler should be auto started. | true | boolean |
timeUnit (scheduler) | Time unit for initialDelay and delay options. Enum values:
| MILLISECONDS | TimeUnit |
useFixedDelay (scheduler) | Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details. | true | boolean |
15.4. Endpoint Connection Syntax
The endpoint can initiate the Cassandra connection or use an existing one.
URI | Description |
---|---|
| Single host, default port, usual for testing |
| Multi host, default port |
| Multi host, custom port |
| Default port and keyspace |
| Provided Session reference |
| Provided Cluster reference |
To fine tune the Cassandra connection (SSL options, pooling options, load balancing policy, retry policy, reconnection policy…), create your own Cluster instance and give it to the Camel endpoint.
15.5. Messages
15.5.1. Incoming Message
The Camel Cassandra endpoint expects a bunch of simple objects (Object
or Object[]
or Collection<Object>
) which will be bound to the CQL statement as query parameters. If message body is null or empty, then CQL query will be executed without binding parameters.
Headers
CamelCqlQuery
(optional,String
orRegularStatement
)CQL query either as a plain String or built using the
QueryBuilder
.
15.5.2. Outgoing Message
The Camel Cassandra endpoint produces one or many a Cassandra Row objects depending on the resultSetConversionStrategy
:
-
List<Row>
ifresultSetConversionStrategy
isALL
orLIMIT_[0-9]+
-
Single` Row` if
resultSetConversionStrategy
isONE
-
Anything else, if
resultSetConversionStrategy
is a custom implementation of theResultSetConversionStrategy
15.6. Repositories
Cassandra can be used to store message keys or messages for the idempotent and aggregation EIP.
Cassandra might not be the best tool for queuing use cases yet, read Cassandra anti-patterns queues and queue like datasets. It’s advised to use LeveledCompaction and a small GC grace setting for these tables to allow tombstoned rows to be removed quickly.
15.7. Idempotent repository
The NamedCassandraIdempotentRepository
stores messages keys in a Cassandra table like this:
CAMEL_IDEMPOTENT.cql
CREATE TABLE CAMEL_IDEMPOTENT ( NAME varchar, -- Repository name KEY varchar, -- Message key PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400;
This repository implementation uses lightweight transactions (also known as Compare and Set) and requires Cassandra 2.0.7+.
Alternatively, the CassandraIdempotentRepository
does not have a NAME
column and can be extended to use a different data model.
Option | Default | Description |
---|---|---|
|
| Table name |
|
| Primary key columns |
|
Repository name, value used for | |
| Key time to live | |
|
Consistency level used to insert/delete key: | |
|
Consistency level used to read/check key: |
15.8. Aggregation repository
The NamedCassandraAggregationRepository
stores exchanges by correlation key in a Cassandra table like this:
CAMEL_AGGREGATION.cql
CREATE TABLE CAMEL_AGGREGATION ( NAME varchar, -- Repository name KEY varchar, -- Correlation id EXCHANGE_ID varchar, -- Exchange id EXCHANGE blob, -- Serialized exchange PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400;
Alternatively, the CassandraAggregationRepository
does not have a NAME
column and can be extended to use a different data model.
Option | Default | Description |
---|---|---|
|
| Table name |
|
| Primary key columns |
|
| Exchange Id column |
|
| Exchange content column |
|
Repository name, value used for | |
| Exchange time to live | |
|
Consistency level used to insert/delete exchange: | |
|
Consistency level used to read/check exchange: |
15.9. Examples
To insert something on a table you can use the following code:
String CQL = "insert into camel_user(login, first_name, last_name) values (?, ?, ?)"; from("direct:input") .to("cql://localhost/camel_ks?cql=" + CQL);
At this point you should be able to insert data by using a list as body
Arrays.asList("davsclaus", "Claus", "Ibsen")
The same approach can be used for updating or querying the table.
15.10. Spring Boot Auto-Configuration
When using cql with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-cassandraql-starter</artifactId> </dependency>
The component supports 4 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
camel.component.cql.autowired-enabled | Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. | true | Boolean |
camel.component.cql.bridge-error-handler | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | Boolean |
camel.component.cql.enabled | Whether to enable auto configuration of the cql component. This is enabled by default. | Boolean | |
camel.component.cql.lazy-start-producer | Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. | false | Boolean |