我正在使用
java version "1.7.0_09"
Java(TM) SE Runtime Environment (build 1.7.0_09-b05)
Java HotSpot(TM) 64-Bit Server VM (build 23.5-b02, mixed mode)
与G1垃圾收集器。 JVM论证是
-server -Xss4096k -XX:MaxPermSize=512m -XX:PermSize=512m -Xms30G
-Xmx30G -Xnoclassgc -XX:+UseNUMA -XX:+UseFastAccessorMethods
-XX:ReservedCodeCacheSize=48m -XX:+UseStringCache
-XX:+UseGCOverheadLimit -Duser.timezone=EET
-Xmaxf1 -XX:+UseCompressedOops -XX:+DisableExplicitGC
-XX:+AggressiveOpts -XX:CMSInitiatingOccupancyFraction=70
-XX:+ParallelRefProcEnabled -XX:+UseAdaptiveSizePolicy
-XX:MaxGCPauseMillis=500 -XX:+UseG1GC
-XX:InitiatingHeapOccupancyPercent=0
-XX:GCPauseIntervalMillis=10000 -XX:+PrintGCDetails
-XX:+PrintHeapAtGC -XX:+PrintGCDateStamps -Xloggc:gc.log
但是，我正在经历完全GC扫描而没有任何明显的原因，如何摆脱它们？
GC日志，其中包含前面事件的尾部：
{Heap before GC invocations=206 (full 8):
garbage-first heap total 31457280K, used 18323299K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 768 young (6291456K), 31 survivors (253952K)
compacting perm gen total 524288K, used 145771K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465af18, 0x00007fce7465b000, 0x00007fce8b800000)
No shared spaces configured.
2013-01-16T11:45:31.290+0200: 20430.451: [GC pause (young), 0.54738500 secs]
[Parallel Time: 510.7 ms]
[GC Worker Start (ms): 20430451.7 20430451.8 20430451.8 20430451.8
Avg: 20430451.8, Min: 20430451.7, Max: 20430451.8, Diff: 0.1]
[Ext Root Scanning (ms): 22.3 68.3 21.8 20.8
Avg: 33.3, Min: 20.8, Max: 68.3, Diff: 47.5]
[Update RS (ms): 21.6 0.0 23.6 23.7
Avg: 17.3, Min: 0.0, Max: 23.7, Diff: 23.7]
[Processed Buffers : 77 0 18 55
Sum: 150, Avg: 37, Min: 0, Max: 77, Diff: 77]
[Scan RS (ms): 19.6 0.1 19.3 19.6
Avg: 14.7, Min: 0.1, Max: 19.6, Diff: 19.5]
[Object Copy (ms): 439.1 434.2 437.8 438.4
Avg: 437.4, Min: 434.2, Max: 439.1, Diff: 4.9]
[Termination (ms): 0.0 0.0 0.0 0.0
Avg: 0.0, Min: 0.0, Max: 0.0, Diff: 0.0]
[Termination Attempts : 1 1 1 1
Sum: 4, Avg: 1, Min: 1, Max: 1, Diff: 0]
[GC Worker End (ms): 20430954.5 20430954.6 20430954.5 20430954.4
Avg: 20430954.5, Min: 20430954.4, Max: 20430954.6, Diff: 0.1]
[GC Worker (ms): 502.7 502.8 502.7 502.6
Avg: 502.7, Min: 502.6, Max: 502.8, Diff: 0.2]
[GC Worker Other (ms): 8.0 8.0 8.0 8.1
Avg: 8.0, Min: 8.0, Max: 8.1, Diff: 0.1]
[Clear CT: 2.6 ms]
[Other: 34.1 ms]
[Choose CSet: 0.1 ms]
[Ref Proc: 27.4 ms]
[Ref Enq: 0.2 ms]
[Free CSet: 5.4 ms]
[Eden: 5896M(5896M)->0B(5688M) Survivors: 248M->456M Heap: 17893M(30720M)->12208M(30720M)]
[Times: user=2.12 sys=0.02, real=0.55 secs]
Heap after GC invocations=207 (full 8):
garbage-first heap total 31457280K, used 12501684K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 57 young (466944K), 57 survivors (466944K)
compacting perm gen total 524288K, used 145771K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465af18, 0x00007fce7465b000, 0x00007fce8b800000)
No shared spaces configured.
}
{Heap before GC invocations=207 (full 8):
garbage-first heap total 31457280K, used 19058524K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 727 young (5955584K), 57 survivors (466944K)
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000)
No shared spaces configured.
2013-01-16T11:46:26.619+0200: 20485.781: [GC pause (mixed), 1.42356500 secs]
[Parallel Time: 1385.9 ms]
[GC Worker Start (ms): 20485786.6 20485786.6 20485786.6 20485786.7
Avg: 20485786.6, Min: 20485786.6, Max: 20485786.7, Diff: 0.1]
[Ext Root Scanning (ms): 22.1 70.0 22.2 21.3
Avg: 33.9, Min: 21.3, Max: 70.0, Diff: 48.7]
[Update RS (ms): 9.9 0.0 10.9 11.2
Avg: 8.0, Min: 0.0, Max: 11.2, Diff: 11.2]
[Processed Buffers : 13 0 25 17
Sum: 55, Avg: 13, Min: 0, Max: 25, Diff: 25]
[Scan RS (ms): 324.6 276.4 324.6 324.6
Avg: 312.5, Min: 276.4, Max: 324.6, Diff: 48.2]
[Object Copy (ms): 1021.1 1031.2 1019.8 1020.5
Avg: 1023.1, Min: 1019.8, Max: 1031.2, Diff: 11.4]
[Termination (ms): 0.0 0.0 0.0 0.0
Avg: 0.0, Min: 0.0, Max: 0.0, Diff: 0.0]
[Termination Attempts : 6 5 5 1
Sum: 17, Avg: 4, Min: 1, Max: 6, Diff: 5]
[GC Worker End (ms): 20487164.3 20487164.3 20487164.3 20487164.3
Avg: 20487164.3, Min: 20487164.3, Max: 20487164.3, Diff: 0.0]
[GC Worker (ms): 1377.7 1377.6 1377.6 1377.6
Avg: 1377.7, Min: 1377.6, Max: 1377.7, Diff: 0.1]
[GC Worker Other (ms): 8.2 8.3 8.3 8.3
Avg: 8.3, Min: 8.2, Max: 8.3, Diff: 0.1]
[Clear CT: 4.4 ms]
[Other: 33.3 ms]
[Choose CSet: 5.5 ms]
[Ref Proc: 5.0 ms]
[Ref Enq: 0.2 ms]
[Free CSet: 9.1 ms]
[Eden: 5360M(5688M)->0B(5784M) Survivors: 456M->360M Heap: 18616M(30720M)->11359M(30720M)]
[Times: user=5.56 sys=0.01, real=1.42 secs]
Heap after GC invocations=208 (full 8):
garbage-first heap total 31457280K, used 11632594K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 45 young (368640K), 45 survivors (368640K)
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000)
No shared spaces configured.
}
{Heap before GC invocations=208 (full 8):
garbage-first heap total 31457280K, used 11632594K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 45 young (368640K), 45 survivors (368640K)
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000)
No shared spaces configured.
2013-01-16T11:46:28.060+0200: 20487.222: [Full GC 11359M->8807M(30720M), 32.4879420 secs]
[Times: user=45.41 sys=0.21, real=32.48 secs]
Heap after GC invocations=209 (full 9):
garbage-first heap total 31457280K, used 9019206K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000)
the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000)
No shared spaces configured.
}
其他类似的：
{Heap before GC invocations=105 (full 4):
garbage-first heap total 31457280K, used 12638024K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 56 young (458752K), 56 survivors (458752K)
compacting perm gen total 524288K, used 147352K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 28% used [0x00007fd2a2800000, 0x00007fd2ab7e61f8, 0x00007fd2ab7e6200, 0x00007fd2c2800000)
No shared spaces configured.
2013-01-14T10:31:31.240+0200: 14185.812: [Full GC 12341M->7092M(30720M), 25.3417840 secs]
[Times: user=35.12 sys=0.21, real=25.33 secs]
Heap after GC invocations=106 (full 5):
garbage-first heap total 31457280K, used 7262578K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 147352K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 28% used [0x00007fd2a2800000, 0x00007fd2ab7e61f8, 0x00007fd2ab7e6200, 0x00007fd2c2800000)
No shared spaces configured.
}
{Heap before GC invocations=248 (full 11):
garbage-first heap total 31457280K, used 12262418K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 37 young (303104K), 37 survivors (303104K)
compacting perm gen total 524288K, used 152608K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abd082e8, 0x00007fd2abd08400, 0x00007fd2c2800000)
No shared spaces configured.
2013-01-14T13:01:39.869+0200: 23194.441: [Full GC 11975M->7331M(30720M), 28.6147390 secs]
[Times: user=40.31 sys=0.03, real=28.62 secs]
Heap after GC invocations=249 (full 12):
garbage-first heap total 31457280K, used 7507920K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 152608K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abd082e8, 0x00007fd2abd08400, 0x00007fd2c2800000)
No shared spaces configured.
}
{Heap before GC invocations=399 (full 19):
garbage-first heap total 31457280K, used 13016093K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 54 young (442368K), 54 survivors (442368K)
compacting perm gen total 524288K, used 155475K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abfd4c70, 0x00007fd2abfd4e00, 0x00007fd2c2800000)
No shared spaces configured.
2013-01-14T15:31:36.484+0200: 32191.056: [Full GC 12711M->7543M(30720M), 29.5013210 secs]
[Times: user=41.39 sys=0.06, real=29.50 secs]
Heap after GC invocations=400 (full 20):
garbage-first heap total 31457280K, used 7724994K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 155475K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abfd4c70, 0x00007fd2abfd4e00, 0x00007fd2c2800000)
No shared spaces configured.
}
{Heap before GC invocations=476 (full 26):
garbage-first heap total 31457280K, used 14622246K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 27 young (221184K), 27 survivors (221184K)
compacting perm gen total 524288K, used 156716K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac10b2b0, 0x00007fd2ac10b400, 0x00007fd2c2800000)
No shared spaces configured.
2013-01-14T18:46:41.545+0200: 43896.117: [Full GC 14279M->8107M(30720M), 31.6936770 secs]
[Times: user=44.40 sys=0.18, real=31.69 secs]
Heap after GC invocations=477 (full 27):
garbage-first heap total 31457280K, used 8302054K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 156551K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac0e1fa0, 0x00007fd2ac0e2000, 0x00007fd2c2800000)
No shared spaces configured.
}
{Heap before GC invocations=522 (full 34):
garbage-first heap total 31457280K, used 16096219K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 30 young (245760K), 30 survivors (245760K)
compacting perm gen total 524288K, used 156869K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac1315d8, 0x00007fd2ac131600, 0x00007fd2c2800000)
No shared spaces configured.
2013-01-14T22:31:40.711+0200: 57395.283: [Full GC 15718M->11933M(30720M), 42.0857250 secs]
[Times: user=60.13 sys=0.07, real=42.08 secs]
Heap after GC invocations=523 (full 35):
garbage-first heap total 31457280K, used 12219927K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000)
region size 8192K, 0 young (0K), 0 survivors (0K)
compacting perm gen total 524288K, used 156869K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000)
the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac1315d8, 0x00007fd2ac131600, 0x00007fd2c2800000)
No shared spaces configured.
}
其他类似的问题报告：
http://grokbase.com/t/openjdk/hotspot-gc-use/1192sy84j5/g1c-strange-full-gc-behavior http://grokbase.com/p/openjdk/hotspot-gc-use/123ydf9c92/puzzling-why-is-a-full-gc-triggered-here http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2013-February/001484.html
我一直在使用appdynamics探测器分析这个问题，我发现每次Full GC发生时，Code Cache（配置为最大值）都已满。这似乎是GC中的一个错误。
另请参见探查器图像，两个不必要的Full GC：在24/5和25/5之间的中间位置。更重要的是，它们会破坏服务器的可用性，因为它们每个都会持续60秒：
Profiler log image http://eisler.vps.kotisivut.com/logs/g1gc-code-cache-full-gc-bug-illustration.png
另见关于Azul暂停GC的讨论，他们似乎已经解决了这类问题http://www.artima.com/lejava/articles/azul_pauseless_gc.html
答案 0 :(得分：7)
请参阅我的回复 G1GC long pause with initial-mark
你的每一个环境应该有充分的理由来到这里......不幸的是，有些人没有这样的设施。 -XX:+UseBiasedLocking (used for combination of tenured and young generation GCs, but G1GC is capable to handle both) -XX:+DisableExplicitGC (its unpredictable, in my experience its never restrict explicit gc calls)
请在下面提到的设置中使用/调整以获得最佳效果，我将为您提供前进基线，希望这些设置对您有用： Java G1 garbage collection in production
答案 1 :(得分：5)
我们在1.7._u06上记录了这个错误，并在几天前升级到1.7.0_21-b11，我们还没有看到自升级以来的任何Full GC，所以看起来这个bug在JVM中得到了修复。在分析器中，代码高速缓存内存配置文件现在看起来也更好。在过去，这个问题曾经是每天一次，每天一次或多次。
如果情况发生变化，我会报告回来。在此之前，我认为升级后问题已解决。
