[Hadoop Wiki] Update of "ZooKeeper/ServiceLatencyOverview" by PatrickHunt

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http://wiki.apache.org/hadoop/ZooKeeper/ServiceLatencyOverview

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== ZooKeeper service latencies under various loads & configurations ==

The intent of this document is to test the performance of various loads on a ZooKeeper service.

=== Hardware ===

All systems were dual quad core Intel(R) Xeon(R) CPUs running at 2.50GHz. Eight cores were available however as noted below Linux's processor affinity feature was used to limit CPU availability to the JVM.

All systems had 16gig memory available, however unless specifically noted the JVM's -Xmx option was used to limit the size of the JVM heap to 512m.

=== OS === 

Linux version 2.6.18-53.1.13.el5 compiled using gcc version 4.1.2 20070626 (Red Hat 4.1.2-14))

=== ZooKeeper Configuration ===

The following basic configuration was used on all serving nodes:

tickTime=2000
initLimit=10
syncLimit=5
dataDir=<data directory>
clientPort=2181

A dedicated log device was not used, the data directory is store on the same device as the operating system, the ZK snapshots and log4j logs.

The standard zkServer.sh script that ships with the release was used to start the service. No modification were made other than to control processor affinity and heap size as noted in this document.

=== Test Client ===

zk-latencies.py from http://github.com/phunt/zk-smoketest was used as the test client.


== Results ==