Red Hat
Jan 8, 2013
by Shane K Johnson

This post highlights three performance tuning techniques for Red Hat Enterprise Linux (6.2) and OpenJDK (1.6): TCP send / receive windows, large page memory, and i-CMS.

These techniques are particularly applicable to data grids or to any distributed system that stores a lot of data.

I just finished a technical white paper on JBoss Data Grid (JDG) performance factors, and these techniques were necessary for JDG to perform at its best.


Set the maximum size of the TCP send / receive windows of the accordingly.

Example: 640K Send Window / 25MB Receive Window

echo 655360 > /proc/sys/net/core/wmem_max
echo 26214400 > /proc/sys/net/core/rmem_max


Configure large page memory. More information about large page memory can be found here.

Example: A server with 16GB of memory with 12.5GB of it reserved for large page memory.

echo 17179869184 > /proc/sys/kernel/shmmax
echo 6400 > /proc/sys/vm/nr_hugepage
echo 500 > /proc/sys/vm/hugetlb_shm_group

Update the resource limits.


jboss      soft   memlock      unlimited
jboss      hard   memlock      unlimited

Set the JVM options.

Note: The heap size (12GB) is less than the amount of memory reserved for large page memory (12.5GB) as the heap is not the only memory used by the JVM.

-Xms12G -Xmx12G

Garbage Collection

Use the Concurrent Mark Sweep (CMS) garbage collector in Incremental mode (i-CMS).

-XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode

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