why this young gc is so slow?

BlueDavy Lin bluedavy at gmail.com
Fri Aug 19 01:57:10 PDT 2011


      CPU: 16 core,   Physical Memory: 24G   JDK: 6u23 || 6u21
      startup options: -Xmn1g -Xms4g -Xmx4g

      some gc log:
      2011-08-19T16:55:27.759+0800: 92.888: [GC [PSYoungGen:
1022368K->22752K(1024320K)] 1073312K->79200K(4170048K), 0.2117400
secs] [Times: user=2.80 sys=0.00, real=0.21 secs]
2011-08-19T16:55:29.377+0800: 94.507: [GC [PSYoungGen:
1022688K->22848K(1024192K)] 1079136K->82896K(4169920K), 0.1858340
secs] [Times: user=2.37 sys=0.01, real=0.18 secs]
2011-08-19T16:55:30.999+0800: 96.128: [GC [PSYoungGen:
1022784K->22784K(1024448K)] 1082832K->84752K(4170176K), 0.1648320
secs] [Times: user=1.98 sys=0.00, real=0.16 secs]
2011-08-19T16:55:32.576+0800: 97.706: [GC [PSYoungGen:
1023040K->22816K(1024384K)] 1085008K->89416K(4170112K), 0.1979820
secs] [Times: user=2.56 sys=0.00, real=0.19 secs]
2011-08-19T16:55:34.194+0800: 99.323: [GC [PSYoungGen:
1023072K->22784K(1024640K)] 1089672K->92208K(4170368K), 0.1748660
secs] [Times: user=2.18 sys=0.01, real=0.18 secs]
2011-08-19T16:55:35.779+0800: 100.909: [GC [PSYoungGen:
1023360K->22784K(1024512K)] 1092784K->97792K(4170240K), 0.2129800
secs] [Times: user=2.81 sys=0.00, real=0.21 secs]
2011-08-19T16:55:37.437+0800: 102.567: [GC [PSYoungGen:
1023360K->22752K(1024768K)] 1098368K->101528K(4170496K), 0.1880140
secs] [Times: user=2.40 sys=0.00, real=0.18 secs]
2011-08-19T16:55:39.040+0800: 104.169: [GC [PSYoungGen:
1023648K->22784K(1024704K)] 1102424K->103688K(4170432K), 0.1647610
secs] [Times: user=2.01 sys=0.01, real=0.16 secs]
2011-08-19T16:55:40.605+0800: 105.735: [GC [PSYoungGen:
1023680K->22816K(1024896K)] 1104584K->108600K(4170624K), 0.2030000
secs] [Times: user=2.65 sys=0.00, real=0.21 secs]

       I think for ps gc,the live objects is the key factor,but in
this case,live objects are not so much,why gc time so slow?  I think
it should be below 20ms,can someone help me for this?

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