Seeking answer to a GC pattern

[Jun Zhuang]

Hi,

When running performance testing for a java web service running on JBOSS, I observed a clear saw-tooth pattern in CPU utilization that closely follows the GC cycles. see below:

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Java startup parameters used:

-XX:+TieredCompilation -XX:+PrintTenuringDistribution -Xms2048m -Xmx4096m -XX:MaxPermSize=256m -XX:NewSize=128m -XX:MaxNewSize=128m -XX:SurvivorRatio=126 -XX:-UseAdaptiveSizePolicy -XX:+DisableExplicitGC -XX:+AlwaysTenure

With this set of parameters, the young GC pause time ranged from 0.02 to 0.25 secs. When I used 256m for the young gen, the young GC pause time ranged from 0.02 to 0.5 secs. My understanding is that the young GC pause time normally stays fairly stable, I have spent quite some time researching but have yet to find an answer to this behavior. I wonder if people in this distribution list can help me out?

Other related info

* Server Specs: VM with 4 CPUs and 8 Gb mem
* Test setup:

*         # of Vusers: 100

*         Ramp up: 10 mins

*         Pacing: 5 - 7 secs
* I tried with all other available GC algorithms, tenuring thresholds, various sizes of the generations, but the AlwaysTenure parameter seems to work the best so far.

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Any input will be highly appreciated.

Sincerely yours,

Jun Zhuang
Sr. Performance QA Engineer | Hobsons
513-746-2288 (work)
513-227-7643 (mobile)

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