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Cassandra is a highly-scalable, eventually consistent, distributed, structured key-value store which acts as the persistence storage for WSO2 MB.

Installation Prerequisites

Cassandra requires the most stable version of Java 1.6 for Sun JVM. (u19 or higher is recommended. u21 is best). For instructions on installing Java, refer to

Download Cassandra Kit

Edit Configuration Files

Cassandra configuration files can be found in $CARBON_HOME/repository/conf/etc directory of binary and source distributions. If you have installed Cassandra from RPM packages, configuration files will be placed into /etc/cassandra/conf. Cassandra configurations can be done in the following files.

Edit cassandra.yaml

The default cassandra.yaml contains reasonable settings for single node operation. There are few settings that need to be verified:

  • Ensure that the paths exist for data_file_directories, commitlog_directory, and saved_caches_directory.  
  • Verify storage_port and rpc_port do not conflict with other services on your computer.  By default, Cassandra uses 7000 for storage_port, and 9160 for rpc_port. The storage_port must be identical between Cassandra nodes in a cluster. Cassandra client applications use rpc_port to connect to Cassandra.  
  • It is recommended to change the default cluster_name to avoid conflicts with existing clusters.
  • initial_token can be left blank, but setting to 0 is recommended if you are configuring your first node.

Edit log4j-server.properties

$CARBON_HOME/repository/conf/log4j.properties file contains a path for the log file as required.

# Edit the next line to point to your logs directory
log4j.appender.R.File=/var/log/cassandra/system.log

Edit cassandra-env.sh

By default, Cassandra allocates memory based on the physical memory capacity of your system.  For example, it will allocate 1GB heap on 2GB system, and 2GB heap on 8GB system. To specify Cassandra heap size, remove leading pound sign(#) on the following lines and specify memory size for them.

#MAX_HEAP_SIZE="4G"
#HEAP_NEWSIZE="800M"

If you are not familiar with Java GC, 1/4 of MAX_HEAP_SIZE may be a good start point for HEAP_NEWSIZE. 

Although Cassandra can be run on smaller footprint for test drive, it needs more Giga Bytes of heap for production. For example, to assign 128MB as maximum, edit the lines as follows.

MAX_HEAP_SIZE="128M"
HEAP_NEWSIZE="32M"

It is recommend to use at least "2048M" for MAX_HEAP_SIZE. In case of OutOfMemory exceptions (http://wiki.apache.org/cassandra/OutOfMemory) or massive GCs with this configuration, increase these values. 

Note

Don't start production services with small heap configurations.

Start Cassandra

Cassandra can be started by invoking bin/cassandra -f from the command line. The -f option enures that the service starts in the foreground and logs gratuitously to standard-out. If there are no messages with "errors", or words such as  "fatal" or that look like a Java stack traces, then you've succeeded. After starting the Cassandra server, it starts listening for thrift clients as follows.

....
....
....
INFO 12:18:29,140 Listening for thrift clients...

Press "Control-C" to stop Cassandra.  If you start up Cassandra without "-f" option, it runs in the background, so you need to kill the process to stop.

 

Instruct WSO2 MB to Use External Cassandra Server

    <clustering>
        <enabled>false</enabled>       
        <OnceInOrderSupportEnabled>false</OnceInOrderSupportEnabled>
         <!--Are we running an External Cassandra server ? true|false-->
        <externalCassandraServerRequired>true</externalCassandraServerRequired>
        <!--Are we running an External Zookeeper server ? true|false -->
         <!--externalZookeeperServerRequired>false</externalZookeeperServerRequired-->

 

Point WSO2 MB to Cassandra

Edit $CARBON_HOME/repository/conf/advanced/qpid-virtualhosts.xml file to point to Cassandra server setup.

 <virtualhost>
        <name>carbon</name>
        <carbon>
           <store>
                <class>org.wso2.andes.server.store.CassandraMessageStore</class>
                <username>admin</username>
                <password>admin</password>
                <cluster>ClusterOne</cluster>
                <idGenerator>org.wso2.andes.server.cluster.coordination.TimeStampBasedMessageIdGenerator</idGenerator>
                <connectionString>localhost:9160</connectionString>
            </store>
...
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