64-bit version performance tuning tips

Applications that run on the WAS 64-bit version can see significant performance gains if they can leverage the support for large heaps.

Description: To exploit the large heap, you can use dynamic cache in WAS. The process to tune dynamic cache remains the same for the 64-bit version as for the 32-bit version. However, all memory references are also 64-bit wide on the 64-bit version, which is twice the size of memory references on the 32-bit version. This size difference causes an increase in the memory requirements of the applications when deployed on 64-bit, as compared to 32-bit.

Recommendation: Tune the JVM heap for the appserver according to the previously stated facts. If possible, tune the JVM heap by running the application in test mode, under simulated load with verbose GC turned on. Then, tune the JVM heap to reach a GC cycle rate between five and twenty percent of the total running time. Typically, the application memory footprint can increase by approximately sixty percent.

Another possible side-effect of the memory footprint increase is a decrease in the hardware cache efficiency of the processor. To mitigate this possibility, use processors with large L2 and L3 caches. To learn about the performance of WAS on 64-bit platforms in more detail, refer to IBM WAS and 64-bit platforms - 64-bit performance.

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Related tasks

Tuning the application serving environment

 

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