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Cassandra configuration

Requirements

This directory sets up a Cassandra NoSQL server.

Setup

This setup relies on the host system having Cassandra installed, we merely provide configuration as needed.

On Ubuntu 16.04 issue the following commands as root:

# Installing dependencies and Java 8, accepting prompts
apt-get install software-properties-common curl
add-apt-repository ppa:webupd8team/java
apt-get update
apt-get install oracle-java8-installer

# install Cassandra 3.0.14, from http://cassandra.apache.org/download/
echo "deb http://www.apache.org/dist/cassandra/debian 30x main" | tee -a /etc/apt/sources.list.d/cassandra.sources.list
curl https://www.apache.org/dist/cassandra/KEYS | apt-key add -
apt-get update
apt-get install cassandra

If you configure cassandra to listen to a public IP address, please do protect this cluster with a firewall to prevent unauthorised access!

To change the default listen address for Cassandra (localhost), edit /etc/cassandra/cassandra.yaml to replace the listen_address configuration with listen_address <desired_ip_address>. If planning to deploy Cassandra on the same machine as uWSGI, this parameter does not need changing.

There seems to be an issue with cassandra expecting the output of hostname to resolve to either an ipv4 address or to localhost; if you see an error about Local host name unknown: java.net.UnknownHostException in /var/log/cassandra/system.log, add hostname to /etc/hosts for the 127.0.0.1 entry.

Performance configuration

In order to increase the performance of your Cassandra deployment, the following parameters in /etc/cassandra/cassandra.yaml can be changed:

concurrent_reads: 64
concurrent_writes: 128
concurrent_counter_writes: 128

The values above are suitable for a 2-socket Broadwell-EP server with 22 cores per socket, with all services running on the same machine (Memcached, Cassandra, uWSGI). These values might need to be changed depending on the platform.

Because the concurrent_materialized_view_writes feature is not necessary for the Django Workload, it should be commented out:

#concurrent_materialized_view_writes: 32

The JVM settings can also be adjusted for better performance, by using the following options in /etc/cassandra/jvm.options:

-XX:+UseThreadPriorities
-XX:ThreadPriorityPolicy=42

# Heap size (Xms, Xmx) and young generation size (Xmn) should be set depending
# on the amount of available memory. These settings work for a memory size of 128GB
-Xms65536M
-Xmx65536M
-Xmn16384M

-XX:+HeapDumpOnOutOfMemoryError
-Xss256k
-XX:StringTableSize=1000003

# CMS settings
-XX:+UseParNewGC
-XX:+UseConcMarkSweepGC
-XX:+CMSParallelRemarkEnabled
-XX:SurvivorRatio=4
-XX:MaxTenuringThreshold=1
-XX:CMSInitiatingOccupancyFraction=60
-XX:+UseCMSInitiatingOccupancyOnly

-XX:+CMSScavengeBeforeRemark
-XX:CMSMaxAbortablePrecleanTime=60000

-XX:CMSWaitDuration=30000
-XX:+CMSParallelInitialMarkEnabled
-XX:+CMSEdenChunksRecordAlways
-XX:+CMSClassUnloadingEnabled

# Additional settings
-XX:+UseCondCardMark
-XX:MaxTenuringThreshold=2
-XX:-UseBiasedLocking
-XX:+UseTLAB
-XX:+ResizeTLAB
-XX:+PerfDisableSharedMem
-XX:+AlwaysPreTouch
-XX:+UnlockDiagnosticVMOptions
-XX:ParGCCardsPerStrideChunk=4096

Logging

If needed, logging can be enabled for Cassandra by adding the following flags to /etc/cassandra/jvm.options:

# Logging
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintTenuringDistribution
-XX:+PrintGCApplicationStoppedTime
-XX:+PrintPromotionFailure
-XX:+PrintClassHistogramBeforeFullGC
-XX:+PrintClassHistogramAfterFullGC
-Xloggc:/var/log/cassandra/gc.log
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=2
-XX:GCLogFileSize=10M