我正在使用以下版本的java运行tomcat的大型实例：
java版“1.6.0_20”
OpenJDK运行时环境（IcedTea6 1.9.7）（6b20-1.9.7-0ubuntu1~10.04.1
OpenJDK 64位服务器VM（版本19.0-b09，混合模式）
并使用以下参数设置：
-Xms13152m
-Xmx13152m
-Xmn768m
-XX:+UseConcMarkSweepGC
-XX:CMSInitiatingOccupancyFraction=60
-XX:+CMSIncrementalMode
-XX:+CMSIncrementalPacing
-XX:CMSIncrementalDutyCycleMin=0
-XX:CMSIncrementalDutyCycle=10
-XX:+DisableExplicitGC
启用GC调试语句。每隔几个小时，我就会看到发生次要GC并且应用程序停止很长时间的行为，但GC本身似乎没有花费那么多时间：
{Heap before GC invocations=392 (full 74):
par new generation total 707840K, used 698252K [0x00000004bfa00000, 0x00000004efa00000, 0x00000004efa00000)
eden space 629248K, 99% used [0x00000004bfa00000, 0x00000004e607de48, 0x00000004e6080000)
from space 78592K, 87% used [0x00000004ead40000, 0x00000004ef0a5370, 0x00000004efa00000)
to space 78592K, 0% used [0x00000004e6080000, 0x00000004e6080000, 0x00000004ead40000)
concurrent mark-sweep generation total 12681216K, used 10877603K [0x00000004efa00000, 0x00000007f5a00000, 0x00000007f5a00000)
concurrent-mark-sweep perm gen total 50260K, used 30106K [0x00000007f5a00000, 0x00000007f8b15000, 0x0000000800000000)
13120.154: [GC 13120.154: [ParNew Desired survivor size 40239104 bytes, new threshold 1 (max 4) - age 1: 41912720 bytes, 41912720 total: 698252K->41387K(707840K), 0.1239080 secs] 11575856K->10987714K(13389056K) icms_dc=20 , 0.1239930 secs] [Times: user=0.00 sys=0.00, real=0.12 secs]
Heap after GC invocations=393 (full 74):
par new generation total 707840K, used 41387K [0x00000004bfa00000, 0x00000004efa00000, 0x00000004efa00000)
eden space 629248K, 0% used [0x00000004bfa00000, 0x00000004bfa00000, 0x00000004e6080000)
from space 78592K, 52% used [0x00000004e6080000, 0x00000004e88eace0, 0x00000004ead40000)
to space 78592K, 0% used [0x00000004ead40000, 0x00000004ead40000, 0x00000004efa00000)
concurrent mark-sweep generation total 12681216K, used 10946327K [0x00000004efa00000, 0x00000007f5a00000, 0x00000007f5a00000)
concurrent-mark-sweep perm gen total 50260K, used 30106K [0x00000007f5a00000, 0x00000007f8b15000, 0x0000000800000000)
}
Total time for which application threads were stopped: 32.1614890 seconds
在这种情况下，我希望GC最多停止申请.12秒。有谁知道为什么应用程序停止时间和GC时间之间存在如此巨大的差异？
UPDATE 我已经在GClog中添加了一个更长的片段：
{Heap before GC invocations=201 (full 18):
par new generation total 707840K, used 639557K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 100% used [0x00000004c4e00000, 0x00000004eb480000, 0x00000004eb480000)
from space 78592K, 13% used [0x00000004eb480000, 0x00000004ebe917e8, 0x00000004f0140000)
to space 78592K, 0% used [0x00000004f0140000, 0x00000004f0140000, 0x00000004f4e00000)
concurrent mark-sweep generation total 12681216K, used 6634693K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 28977K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
2011-04-12T18:42:16.450+0000: 12770.352: [GC 12770.352: [ParNew
Desired survivor size 40239104 bytes, new threshold 15 (max 15)
- age 1: 3701392 bytes, 3701392 total
- age 2: 517360 bytes, 4218752 total
- age 3: 2113840 bytes, 6332592 total
- age 4: 3489008 bytes, 9821600 total
: 639557K->12278K(707840K), 0.0948620 secs] 7274251K->6646972K(13389056K) icms_dc=0 , 0.0949550 secs] [Times: user=0.00 sys=0.00, real=0.10 secs]
Heap after GC invocations=202 (full 18):
par new generation total 707840K, used 12278K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 0% used [0x00000004c4e00000, 0x00000004c4e00000, 0x00000004eb480000)
from space 78592K, 15% used [0x00000004f0140000, 0x00000004f0d3dbf0, 0x00000004f4e00000)
to space 78592K, 0% used [0x00000004eb480000, 0x00000004eb480000, 0x00000004f0140000)
concurrent mark-sweep generation total 12681216K, used 6634693K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 28977K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
}
Total time for which application threads were stopped: 0.0952670 seconds
Application time: 5.0191420 seconds
Total time for which application threads were stopped: 0.0001670 seconds
Application time: 2.2198130 seconds
Total time for which application threads were stopped: 0.0004480 seconds
Application time: 5.5295710 seconds
Total time for which application threads were stopped: 0.0001950 seconds
Application time: 0.0097140 seconds
Total time for which application threads were stopped: 0.0000530 seconds
Application time: 7.1299730 seconds
Total time for which application threads were stopped: 0.0001610 seconds
Application time: 12.0198160 seconds
Total time for which application threads were stopped: 0.0001550 seconds
Application time: 1.5298610 seconds
Total time for which application threads were stopped: 0.0001630 seconds
Application time: 0.0097650 seconds
Total time for which application threads were stopped: 0.0000590 seconds
Application time: 0.1199330 seconds
Total time for which application threads were stopped: 0.0000550 seconds
Application time: 10.0998880 seconds
Total time for which application threads were stopped: 0.0003490 seconds
Application time: 1.0093980 seconds
Total time for which application threads were stopped: 0.0003040 seconds
Application time: 0.6099830 seconds
Total time for which application threads were stopped: 0.0001700 seconds
Application time: 0.0298490 seconds
Total time for which application threads were stopped: 0.0000930 seconds
Application time: 0.2025080 seconds
Total time for which application threads were stopped: 0.0023430 seconds
Application time: 0.0190510 seconds
Total time for which application threads were stopped: 0.0003010 seconds
Application time: 0.1793310 seconds
Total time for which application threads were stopped: 0.0002150 seconds
Application time: 0.0560830 seconds
Total time for which application threads were stopped: 0.0010000 seconds
Application time: 1.7072960 seconds
{Heap before GC invocations=202 (full 18):
par new generation total 707840K, used 641302K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 99% used [0x00000004c4e00000, 0x00000004eb447fd8, 0x00000004eb480000)
from space 78592K, 15% used [0x00000004f0140000, 0x00000004f0d3dbf0, 0x00000004f4e00000)
to space 78592K, 0% used [0x00000004eb480000, 0x00000004eb480000, 0x00000004f0140000)
concurrent mark-sweep generation total 12681216K, used 6634693K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29039K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
2011-04-12T18:43:04.052+0000: 12817.954: [GC 12817.955: [ParNew
Desired survivor size 40239104 bytes, new threshold 4 (max 15)
- age 1: 36162128 bytes, 36162128 total
- age 2: 2531664 bytes, 38693792 total
- age 3: 420840 bytes, 39114632 total
- age 4: 2052544 bytes, 41167176 total
- age 5: 3484040 bytes, 44651216 total
: 641302K->44375K(707840K), 0.2037750 secs] 7275996K->6679069K(13389056K) icms_dc=0 , 0.2039060 secs] [Times: user=0.00 sys=0.00, real=0.21 secs]
Heap after GC invocations=203 (full 18):
par new generation total 707840K, used 44375K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 0% used [0x00000004c4e00000, 0x00000004c4e00000, 0x00000004eb480000)
from space 78592K, 56% used [0x00000004eb480000, 0x00000004edfd5f88, 0x00000004f0140000)
to space 78592K, 0% used [0x00000004f0140000, 0x00000004f0140000, 0x00000004f4e00000)
concurrent mark-sweep generation total 12681216K, used 6634693K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29039K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
}
Total time for which application threads were stopped: 0.2043140 seconds
Application time: 0.0001040 seconds
Total time for which application threads were stopped: 0.0000890 seconds
Application time: 4.0399400 seconds
{Heap before GC invocations=203 (full 18):
par new generation total 707840K, used 673623K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 100% used [0x00000004c4e00000, 0x00000004eb480000, 0x00000004eb480000)
from space 78592K, 56% used [0x00000004eb480000, 0x00000004edfd5f88, 0x00000004f0140000)
to space 78592K, 0% used [0x00000004f0140000, 0x00000004f0140000, 0x00000004f4e00000)
concurrent mark-sweep generation total 12681216K, used 6634693K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29040K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
2011-04-12T18:44:23.258+0000: 12897.160: [GC 12897.160: [ParNew
Desired survivor size 40239104 bytes, new threshold 1 (max 15)
- age 1: 46278472 bytes, 46278472 total
- age 2: 23234248 bytes, 69512720 total
- age 3: 2144024 bytes, 71656744 total
- age 4: 391464 bytes, 72048208 total
: 673623K->78592K(707840K), 0.1607580 secs] 7308317K->6752580K(13389056K) icms_dc=0 , 0.1608520 secs] [Times: user=0.00 sys=0.00, real=0.16 secs]
Heap after GC invocations=204 (full 18):
par new generation total 707840K, used 78592K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 0% used [0x00000004c4e00000, 0x00000004c4e00000, 0x00000004eb480000)
from space 78592K, 100% used [0x00000004f0140000, 0x00000004f4e00000, 0x00000004f4e00000)
to space 78592K, 0% used [0x00000004eb480000, 0x00000004eb480000, 0x00000004f0140000)
concurrent mark-sweep generation total 12681216K, used 6673988K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29040K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
}
Total time for which application threads were stopped: 75.1222720 seconds
Application time: 0.0660880 seconds
Total time for which application threads were stopped: 0.0001500 seconds
Application time: 0.0001110 seconds
Total time for which application threads were stopped: 0.0000620 seconds
Application time: 0.0000320 seconds
Total time for which application threads were stopped: 0.0000620 seconds
Application time: 0.5790490 seconds
Total time for which application threads were stopped: 0.0151370 seconds
Application time: 0.0241790 seconds
Total time for which application threads were stopped: 0.0111420 seconds
Application time: 0.1488160 seconds
Total time for which application threads were stopped: 0.0168360 seconds
Application time: 0.0237110 seconds
Total time for which application threads were stopped: 0.0008580 seconds
Application time: 0.0594260 seconds
Total time for which application threads were stopped: 0.0179450 seconds
Application time: 0.0331740 seconds
Total time for which application threads were stopped: 0.0072850 seconds
Application time: 1.2617710 seconds
{Heap before GC invocations=204 (full 18):
par new generation total 707840K, used 707840K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 100% used [0x00000004c4e00000, 0x00000004eb480000, 0x00000004eb480000)
from space 78592K, 100% used [0x00000004f0140000, 0x00000004f4e00000, 0x00000004f4e00000)
to space 78592K, 0% used [0x00000004eb480000, 0x00000004eb480000, 0x00000004f0140000)
concurrent mark-sweep generation total 12681216K, used 6673988K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29089K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
2011-04-12T18:44:25.690+0000: 12899.592: [GC 12899.592: [ParNew
Desired survivor size 40239104 bytes, new threshold 1 (max 15)
- age 1: 42048296 bytes, 42048296 total
: 707840K->58684K(707840K), 0.1654070 secs] 7381828K->6802196K(13389056K) icms_dc=0 , 0.1655450 secs] [Times: user=0.00 sys=0.00, real=0.17 secs]
Heap after GC invocations=205 (full 18):
par new generation total 707840K, used 58684K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 0% used [0x00000004c4e00000, 0x00000004c4e00000, 0x00000004eb480000)
from space 78592K, 74% used [0x00000004eb480000, 0x00000004eedcf320, 0x00000004f0140000)
to space 78592K, 0% used [0x00000004f0140000, 0x00000004f0140000, 0x00000004f4e00000)
concurrent mark-sweep generation total 12681216K, used 6743511K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29089K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
}
Total time for which application threads were stopped: 0.1709510 seconds
Application time: 1.0183040 seconds
Total time for which application threads were stopped: 0.0009220 seconds
Application time: 0.0209220 seconds
Total time for which application threads were stopped: 0.0009260 seconds
Application time: 0.0181760 seconds
Total time for which application threads were stopped: 0.0002780 seconds
Application time: 0.0773630 seconds
Total time for which application threads were stopped: 0.0019720 seconds
Application time: 0.0045340 seconds
Total time for which application threads were stopped: 0.0001400 seconds
Application time: 0.0245930 seconds
Total time for which application threads were stopped: 0.0004070 seconds
Application time: 0.4811530 seconds
Total time for which application threads were stopped: 0.0043100 seconds
Application time: 0.0015090 seconds
Total time for which application threads were stopped: 0.0052290 seconds
Application time: 0.0264570 seconds
Total time for which application threads were stopped: 0.0072530 seconds
Application time: 0.0135600 seconds
Total time for which application threads were stopped: 0.0121400 seconds
Application time: 0.0278510 seconds
Total time for which application threads were stopped: 0.0078060 seconds
Application time: 0.0136080 seconds
Total time for which application threads were stopped: 0.0121390 seconds
Application time: 0.0066360 seconds
Total time for which application threads were stopped: 0.0004330 seconds
Application time: 0.0107480 seconds
Total time for which application threads were stopped: 0.0001900 seconds
Application time: 0.0027230 seconds
Total time for which application threads were stopped: 0.0132610 seconds
Application time: 0.0126600 seconds
Total time for which application threads were stopped: 0.0003420 seconds
Application time: 0.5384840 seconds
{Heap before GC invocations=205 (full 18):
par new generation total 707840K, used 687932K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 100% used [0x00000004c4e00000, 0x00000004eb480000, 0x00000004eb480000)
from space 78592K, 74% used [0x00000004eb480000, 0x00000004eedcf320, 0x00000004f0140000)
to space 78592K, 0% used [0x00000004f0140000, 0x00000004f0140000, 0x00000004f4e00000)
concurrent mark-sweep generation total 12681216K, used 6743511K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29092K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
2011-04-12T18:44:28.223+0000: 12902.125: [GC 12902.125: [ParNew
Desired survivor size 40239104 bytes, new threshold 15 (max 15)
- age 1: 5906520 bytes, 5906520 total
: 687932K->45478K(707840K), 0.2139570 secs] 7431444K->6860368K(13389056K) icms_dc=0 , 0.2142010 secs] [Times: user=0.00 sys=0.00, real=0.21 secs]
Heap after GC invocations=206 (full 18):
par new generation total 707840K, used 45478K [0x00000004c4e00000, 0x00000004f4e00000, 0x00000004f4e00000)
eden space 629248K, 0% used [0x00000004c4e00000, 0x00000004c4e00000, 0x00000004eb480000)
from space 78592K, 57% used [0x00000004f0140000, 0x00000004f2da9b30, 0x00000004f4e00000)
to space 78592K, 0% used [0x00000004eb480000, 0x00000004eb480000, 0x00000004f0140000)
concurrent mark-sweep generation total 12681216K, used 6814889K [0x00000004f4e00000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 47232K, used 29092K [0x00000007fae00000, 0x00000007fdc20000, 0x0000000800000000)
}
更新
我将我的应用程序切换到多核机器以帮助减轻CMS收集的痛苦，现在，在稳定状态下，我看不到任何暂停。但是，在更新我的搜索索引期间，会很快生成大量大型内存结构，并且应用程序再次遭受长STW暂停。我不确定如何避免这种情况，因为这些物体可能应该存在于终身代，我增加了幸存者空间的大小（-XX：SurvivorRatio = 8），但我仍然观察到长时间停顿。请参阅下面的GC日志：
{Heap before GC invocations=103 (full 48):
par new generation total 921600K, used 912322K [0x000000050ce00000, 0x000000054b600000, 0x000000054b600000)
eden space 819200K, 99% used [0x000000050ce00000, 0x000000053e776380, 0x000000053ee00000)
from space 102400K, 97% used [0x000000053ee00000, 0x0000000544f7a630, 0x0000000545200000)
to space 102400K, 0% used [0x0000000545200000, 0x0000000545200000, 0x000000054b600000)
concurrent mark-sweep generation total 11264000K, used 6486203K [0x000000054b600000, 0x00000007fae00000, 0x00000007fae00000)
concurrent-mark-sweep perm gen total 48516K, used 29211K [0x00000007fae00000, 0x00000007
fdd61000, 0x0000000800000000)
2011-04-14T15:15:25.322+0000: 2358.684: [GC 2358.684: [ParNew
Desired survivor size 52428800 bytes, new threshold 1 (max 15)- age 1: 102164088 bytes, 102164088 total
: 912322K->99941K(921600K), 30.0146400 secs] 7398525K->6818473K(12185600K), 30.0147850 se
cs] [Times: user=0.00 sys=0.00, real=30.02 secs]
Heap after GC invocations=104 (full 48): par new generation total 921600K, used 99941K [0x000000050ce00000, 0x000000054b600000,
0x000000054b600000)
eden space 819200K, 0% used [0x000000050ce00000, 0x000000050ce00000, 0x000000053ee00000)
from space 102400K, 97% used [0x0000000545200000, 0x000000054b399710, 0x000000054b6000
00)
to space 102400K, 0% used [0x000000053ee00000, 0x000000053ee00000, 0x00000005452000
00) concurrent mark-sweep generation total 11264000K, used 6718531K [0x000000054b600000, 0x0
0000007fae00000, 0x00000007fae00000) concurrent-mark-sweep perm gen total 48516K, used 29211K [0x00000007fae00000, 0x00000007
fdd61000, 0x0000000800000000)}
Total time for which application threads were stopped: 30.0152850 seconds
Application time: 0.9450500 seconds
答案 0 :(得分：3)
为较长的GC日志添加了评论
我认为你的幸存者空间太小了，注意伊甸园里的幸存者已经满了56％，之前伊甸园并不满，但幸存者是100％。这意味着它被强制进入一个完全非并发的终身收藏，据报道它是一个年轻的gc，因为它不是由CMS引发的，因为它无处可放多余的垃圾而是终身。只有终身收藏家才能完成任务，因此会触发完整的GC。补救措施是使伊甸园更大和/或使幸存者空间更大。您可以使用SurvivorRatio执行此操作，例如-XX:SurvivorRatio=8表示将每个幸存者空间设置为伊甸园的1/8。
停止时间实际上是“JVM在安全点上花费的时间”，您可以使用PrintSafepointStatistics来确定安全点期间发生的事情。 This post有一个指向操作列表的链接，这些操作会导致VM达到一个安全点，如果你仔细阅读它，就会显示有很多不同的方式可以让它做“无所事事”。不要排除OS时钟转换，因为时间是通过时间周期感知时间戳记录的。
btw pre hotspot17这些时间戳可能不准确。该错误在Bug ID:6782663中描述，该错误在hs17中修复，hs17是6u21的一部分（根据the release notes）。因为你在6月20日，它（30s）甚至可能不是真正的价值。
答案 1 :(得分：1)
在某些情况下，并发收集器将回退到完整的GC，暂停所有内容直到完成。如果我没记错的话，如果应用程序创建了许多需要收集但无法跟上的对象，那么一个小的伊甸园可以触发它。您可能想尝试指定更大的eden（或使用比率，以便它与内存正确缩放）。如果您还没有这些配置选项，可以尝试添加这些配置选项以获取更多GC详细信息：
-Xloggc:gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps
通过查看GC日志并迭代各种选项，我设法消除了我们在大型部署中看到的完整GC事件。每个应用程序都是不同的，但是在这里他们也可以帮助你：
-Xms24g -Xmx24g -XX:MaxPermSize=256m -XX:NewRatio=4 -XX:SurvivorRatio=8
-XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+DisableExplicitGC
-XX:+UseCMSInitiatingOccupancyOnly -XX:+CMSClassUnloadingEnabled
-XX:+CMSScavengeBeforeRemark -XX:CMSInitiatingOccupancyFraction=68
由于我们使用的是32GB以下，我们还使用-XX:+UseCompressedOops来减少64位寻址的开销。此外，我们使用-XX:+UseLargePages来获得更好的性能，但您必须首先为您的操作系统启用大页面支持。