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Chapter 72. Cassandra CQL Component

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Available as of Camel version 2.15

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.

Maven users will need to add the following dependency to their pom.xml:

pom.xml 

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-cassandraql</artifactId>
    <version>x.y.z</version>
    <!-- use the same version as your Camel core version -->
</dependency>

72.1. URI format

The endpoint can initiate the Cassandra connection or use an existing one.

URIDescription

cql:localhost/keyspace

Single host, default port, usual for testing

cql:host1,host2/keyspace

Multi host, default port

cql:host1,host2:9042/keyspace

Multi host, custom port

cql:host1,host2

Default port and keyspace

cql:bean:sessionRef

Provided Session reference

cql:bean:clusterRef/keyspace

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.

72.2. Cassandra Options

The Cassandra CQL component has no options.

The Cassandra CQL endpoint is configured using URI syntax: 

cql:beanRef:hosts:port/keyspace

with the following path and query parameters:

72.2.1. Path Parameters (4 parameters):

NameDescriptionDefaultType

beanRef

beanRef is defined using bean:id

 

String

hosts

Hostname(s) cassansdra server(s). Multiple hosts can be separated by comma.

 

String

port

Port number of cassansdra server(s)

 

Integer

keyspace

Keyspace to use

 

String

72.2.2. Query Parameters (29 parameters):

NameDescriptionDefaultType

cluster (common)

To use the Cluster instance (you would normally not use this option)

 

Cluster

clusterName (common)

Cluster name

 

String

consistencyLevel (common)

Consistency level to use

 

ConsistencyLevel

cql (common)

CQL query to perform. Can be overridden with the message header with key CamelCqlQuery.

 

String

loadBalancingPolicy (common)

To use a specific LoadBalancingPolicy

 

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…​

 

String

session (common)

To use the Session instance (you would normally not use this option)

 

Session

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)

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)

Sets the exchange pattern when the consumer creates an exchange.

 

ExchangePattern

pollStrategy (consumer)

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.

 

PollingConsumerPoll Strategy

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

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. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

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. You can also specify time values using units, such as 60s (60 seconds), 5m30s (5 minutes and 30 seconds), and 1h (1 hour).

1000

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.

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.

 

ScheduledExecutor Service

scheduler (scheduler)

To use a cron scheduler from either camel-spring or camel-quartz2 component

none

ScheduledPollConsumer Scheduler

schedulerProperties (scheduler)

To configure additional properties when using a custom scheduler or any of the Quartz2, Spring based scheduler.

 

Map

startScheduler (scheduler)

Whether the scheduler should be auto started.

true

boolean

timeUnit (scheduler)

Time unit for initialDelay and delay options.

MILLISECONDS

TimeUnit

useFixedDelay (scheduler)

Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details.

true

boolean

72.3. Spring Boot Auto-Configuration

The component supports 2 options, which are listed below.

NameDescriptionDefaultType

camel.component.cql.enabled

Enable cql component

true

Boolean

camel.component.cql.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

72.4. Messages

72.4.1. 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 or RegularStatement): CQL query either as a plain String or built using the QueryBuilder.

72.4.2. Outgoing Message

The Camel Cassandra endpoint produces one or many a Cassandra Row objects depending on the resultSetConversionStrategy:

 

  • List<Row> if resultSetConversionStrategy is ALL or LIMIT_[0-9]+
  • Single` Row` if resultSetConversionStrategy is ONE
  • Anything else, if resultSetConversionStrategy is a custom implementation of the ResultSetConversionStrategy

72.5. 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.

72.6. 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.

OptionDefaultDescription

table

CAMEL_IDEMPOTENT

Table name

pkColumns

NAME,` KEY`

Primary key columns

name

 

Repository name, value used for NAME column

ttl

 

Key time to live

writeConsistencyLevel

 

Consistency level used to insert/delete key: ANY, ONE, TWO, QUORUM, LOCAL_QUORUM…

readConsistencyLevel

 

Consistency level used to read/check key: ONE, TWO, QUORUM, LOCAL_QUORUM…

72.7. 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.

OptionDefaultDescription

table

CAMEL_AGGREGATION

Table name

pkColumns

NAME,KEY

Primary key columns

exchangeIdColumn

EXCHANGE_ID

Exchange Id column

exchangeColumn

EXCHANGE

Exchange content column

name

 

Repository name, value used for NAME column

ttl

 

Exchange time to live

writeConsistencyLevel

 

Consistency level used to insert/delete exchange: ANY, ONE, TWO, QUORUM, LOCAL_QUORUM…

readConsistencyLevel

 

Consistency level used to read/check exchange: ONE, TWO, QUORUM, LOCAL_QUORUM…

72.8. 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.

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