2 Replies Latest reply on May 16, 2012 12:40 PM by Jimy Liu

    Need advice on GC Tuning

    Jimy Liu Newbie



      I am running a performance test on our application.  After the test was run for 1 hour, I see long GC pause which caused response time spikes. Need some help or suggestion on how to reduce the GC pause.

      Here are the GC log :


      2012-05-15T22:52:56.161-0700: 6177.078: [GC 6177.078: [ParNew: 17695592K->1339126K(18874368K), 0.3434470 secs] 43749198K->27457582K(48234496K), 0.3436340 secs]

      [Times: user=5.62 sys=0.02, real=0.34 secs]

      2012-05-15T22:53:05.970-0700: 6186.887: [GC 6186.887: [ParNew: 18115900K->1689020K(18874368K), 0.3852740 secs] 44234355K->27966612K(48234496K), 0.3854630 secs]

      [Times: user=5.47 sys=0.06, real=0.39 secs]

      2012-05-15T22:53:15.642-0700: 6196.558: [GC 6196.558: [ParNew (promotion failed): 18466236K->17822574K(18874368K), 1.5893900 secs]6198.147: [CMS

      : 26715373K->25179454K(29360128K), 56.2166540 secs] 44743828K->25179454K(48234496K), [CMS Perm : 41353K->41229K(69084K)], 57.8062970 secs]

      [Times: user=62.74 sys=0.24, real=57.80 secs]

      2012-05-15T22:54:28.938-0700: 6269.855: [GC 6269.855: [ParNew: 16774330K->778090K(18874368K), 0.0507380 secs] 41953785K->25957545K(48234496K), 0.0509320 secs]

      [Times: user=0.99 sys=0.00, real=0.05 secs]


      2012-05-15T23:46:04.707-0700: 9365.623: [GC 9365.623: [ParNew: 17040515K->359475K(18874368K), 0.0740660 secs] 46306893K->29625853K(48234496K), 0.0741870 secs] [Times: user=1.46 sys=0.00, real=0.08 secs]

      2012-05-15T23:46:05.067-0700: 9365.984: [CMS-concurrent-sweep: 13.441/13.605 secs] [Times: user=142.94 sys=1.38, real=13.60 secs]

      2012-05-15T23:46:05.067-0700: 9365.984: [CMS-concurrent-reset-start]

      2012-05-15T23:46:05.153-0700: 9366.069: [CMS-concurrent-reset: 0.085/0.085 secs] [Times: user=0.73 sys=0.01, real=0.09 secs]

      2012-05-15T23:46:05.432-0700: 9366.348: [GC [1 CMS-initial-mark: 29264165K(29360128K)] 30880704K(48234496K), 0.2924050 secs] [Times: user=0.29 sys=0.00, real=0.29 secs]

      2012-05-15T23:46:05.724-0700: 9366.641: [CMS-concurrent-mark-start]

      2012-05-15T23:46:11.304-0700: 9372.220: [GC 9372.220: [ParNew: 17135902K->301516K(18874368K), 0.1034410 secs] 46400067K->29630497K(48234496K), 0.1035600 secs]

      [Times: user=1.74 sys=0.00, real=0.10 secs]

      2012-05-15T23:46:18.652-0700: 9379.568: [Full GC 9379.568: [CMS

      2012-05-15T23:46:23.919-0700: 9384.835: [CMS-concurrent-mark: 17.954/18.194 secs] [Times: user=206.41 sys=4.01, real=18.19 secs]

      (concurrent mode failure): 29328981K->29057103K(29360128K), 78.5226800 secs] 46405706K->29057103K(48234496K), [CMS Perm : 41177K->41173K(69084K)], 78.5228130 secs] [Times: user=91.91 sys=1.77, real=78.51 secs]


      The server has 24 cores on Linux 64bit OS. JVM version: 1.6.0_24-b07. Here is the JVM options I used:

      -XX:+DisableExplicitGC  -server -Xms48G -Xmx48G -XX:MaxPermSize=728m -Xss128k -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:NewSize=20G -XX:ParallelGCThreads=20 -XX:+PrintGCDateStamps -XX:+PrintGCDetails



      Thanks in advance for any suggestion.



        • 1. Re: Need advice on GC Tuning
          Peter Johnson Master

          Your tenured generation size is too small for using the CMS collector. So it appears that the CMS collector is at some time just giving up and doing a full GC colelction which can be very expensive, as you found out!


          Looking at your post-GC heap size, you have about 700MB in the young gen (in a survivor space) and about 25GB in the tenured gen. Given your heap size (48G heap, 20GB young), you have only 28GB available in the tenured geneation. That gives you only 3GB overhead, or about 10%. I would not have less that 20% overhead, with 25-30% being better. If you can't increase the heap size, decrease the young genaration size, probably down to about 16GB. I also recommend that you reset the survivor space sizes (after the CMS setting). See my white paper numbered "201" at http://www.cmg.org/cgi-bin/search.cgi?q=peter+johnson&x=0&y=0. I cover the CMS collector and tuning it in that paper.

          • 2. Re: Need advice on GC Tuning
            Jimy Liu Newbie



            Thanks for the suggestion. I will make those change and rerun the test.