[[Cassandra-CamelCassandraComponent]]
Camel Cassandra Component
-------------------------

*Available as of Camel 2.15*

http://cassandra.apache.org[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
https://github.com/datastax/java-driver[Cassandra Java Driver] provided
by DataStax.

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

*pom.xml*

[source,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>
------------------------------------------------------------

[[Cassandra-URIformat]]
URI format
~~~~~~~~~~

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

[cols="<,<",options="header",]
|======================================================================
|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.

[[Cassandra-EndpointOptions]]
Endpoint Options
~~~~~~~~~~~~~~~~

[width="100%",cols="<34%,<33%,<33%",options="header",]
|=======================================================================
|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
transformed into message body `ALL`, `ONE`, `LIMIT_10`, `LIMIT_100`...
|=======================================================================

[[Cassandra-Messages]]
Messages
~~~~~~~~

[[Cassandra-IncomingMessage]]
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`.

[[Cassandra-OutgoingMessage]]
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`

[[Cassandra-Repositories]]
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
http://www.datastax.com/dev/blog/cassandra-anti-patterns-queues-and-queue-like-datasets[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.

[[Cassandra-Idempotentrepository]]
Idempotent repository
^^^^^^^^^^^^^^^^^^^^^

The `NamedCassandraIdempotentRepository` stores messages keys in a
Cassandra table like this:

*CAMEL_IDEMPOTENT.cql*

[source,sql]
---------------------------------------------------------
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.

[width="100%",cols="<34%,<33%,<33%",options="header",]
|=======================================================================
|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`…
|=======================================================================

[[Cassandra-Aggregationrepository]]
Aggregation repository
^^^^^^^^^^^^^^^^^^^^^^

The `NamedCassandraAggregationRepository` stores exchanges by
correlation key in a Cassandra table like this:

*CAMEL_AGGREGATION.cql*

[source,sql]
---------------------------------------------------------
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.

[width="100%",cols="<34%,<33%,<33%",options="header",]
|=======================================================================
|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`…
|=======================================================================
