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Chapter 20. Cassandra
Camel Cassandra Component
Available as of Camel 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 a single point of failure and guarantee high availability. Like Google's BigTable, Cassandra data is structured using column families that 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 is based on Cassandra Java Driver provided by DataStax.
Maven users must add the following dependency to their
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>URI format
The endpoint can initiate the Cassandra connection or use an existing one.
| URI | Description |
|---|---|
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.
Endpoint Options
| Option | Default | Description |
|---|---|---|
clusterName
|
Cluster name
|
|
username and password
|
Session authentication
|
|
cql
|
CQL query. Can be overriden with a message header.
|
|
consistencyLevel
|
ANY, ONE, TWO, QUORUM, LOCAL_QUORUM...
|
|
prepareStatements
|
true
|
Use prepared statement (default) or not |
resultSetConversionStrategy
|
ALL
|
How is ResultSet converted and transformed into message body
ALL, ONE, LIMIT_10, LIMIT_100...
|
Messages
Incoming Message
The Camel Cassandra endpoint expects a bunch of simple objects (
Object or Object[] or Collection<Object>) that will be bound to the CQL statement as query parameters. If the message body is null or empty, then the CQL query is executed without binding parameters.
Headers:
CamelCqlQuery(optional,StringorRegularStatement): CQL query either as a plain String or built using theQueryBuilder.
Outgoing Message
The Camel Cassandra endpoint produces one or many Cassandra Row objects depending on the
resultSetConversionStrategy:
List<Row>ifresultSetConversionStrategyisALLorLIMIT_[0-9]+- Single
RowifresultSetConversionStrategyisONE - Anything else, if
resultSetConversionStrategyis a custom implementation of theResultSetConversionStrategy
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 is advised to use LeveledCompaction and a small GC grace setting for these tables to allow tombstoned rows to be removed quickly.
Idempotent repository
The
NamedCassandraIdempotentRepository stores message keys in a Cassandra table like this:
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
|
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…
|
Aggregation repository
The
NamedCassandraAggregationRepository stores exchanges by correlation key in a Cassandra table like this:
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
|
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…
|
