JVM 调优 —— GC 长时间停顿问题及解决方法

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并发模式失败日志： 

2016-02-21T13:53:07.974+0800: 171467.254: [GC [1 CMS-initial-mark: 1436199K(1560576K)] 1512927K(2504320K), 0.0618140 secs] [Times: user=0.06 sys=0.00, real=0.07 secs]
2016-02-21T13:53:08.036+0800: 171467.316: [CMS-concurrent-mark-start]
2016-02-21T13:53:08.377+0800: 171467.657: [CMS-concurrent-mark: 0.340/0.340 secs] [Times: user=2.11 sys=0.15, real=0.34 secs]
2016-02-21T13:53:08.377+0800: 171467.657: [CMS-concurrent-preclean-start]
2016-02-21T13:53:08.385+0800: 171467.665: [CMS-concurrent-preclean: 0.008/0.008 secs] [Times: user=0.01 sys=0.00, real=0.01 secs]
2016-02-21T13:53:08.385+0800: 171467.665: [CMS-concurrent-abortable-preclean-start]
{Heap before GC invocations=88667 (full 45):
 par new generation   total 943744K, used 914399K [0x0000000757000000, 0x0000000797000000, 0x0000000797000000)
  eden space 838912K, 100% used [0x0000000757000000, 0x000000078a340000, 0x000000078a340000)
  from space 104832K,  72% used [0x000000078a340000, 0x000000078ecf7d98, 0x00000007909a0000)
  to   space 104832K,   0% used [0x00000007909a0000, 0x00000007909a0000, 0x0000000797000000)
 concurrent mark-sweep generation total 1560576K, used 1436199K [0x0000000797000000, 0x00000007f6400000, 0x00000007f6400000)
 concurrent-mark-sweep perm gen total 159744K, used 78413K [0x00000007f6400000, 0x0000000800000000, 0x0000000800000000)
2016-02-21T13:53:09.535+0800: 171468.815: [GC2016-02-21T13:53:09.535+0800: 171468.815: [ParNew
Desired survivor size 53673984 bytes, new threshold 6 (max 6)
- age   1:    7100568 bytes,    7100568 total
- age   2:    4676456 bytes,   11777024 total
- age   3:    8773736 bytes,   20550760 total
- age   4:    7709744 bytes,   28260504 total
- age   5:   10891960 bytes,   39152464 total
- age   6:   11735032 bytes,   50887496 total
: 914399K->75616K(943744K), 0.0414860 secs] 2350599K->1517225K(2504320K), 0.0417710 secs] [Times: user=0.32 sys=0.05, real=0.05 secs]
Heap after GC invocations=88668 (full 45):
 par new generation   total 943744K, used 75616K [0x0000000757000000, 0x0000000797000000, 0x0000000797000000)
  eden space 838912K,   0% used [0x0000000757000000, 0x0000000757000000, 0x000000078a340000)
  from space 104832K,  72% used [0x00000007909a0000, 0x0000000795378128, 0x0000000797000000)
  to   space 104832K,   0% used [0x000000078a340000, 0x000000078a340000, 0x00000007909a0000)
 concurrent mark-sweep generation total 1560576K, used 1441609K [0x0000000797000000, 0x00000007f6400000, 0x00000007f6400000)
 concurrent-mark-sweep perm gen total 159744K, used 78413K [0x00000007f6400000, 0x0000000800000000, 0x0000000800000000)
}
2016-02-21T13:53:10.202+0800: 171469.482: [CMS-concurrent-abortable-preclean: 1.772/1.817 secs] [Times: user=4.94 sys=0.06, real=1.81 secs]
2016-02-21T13:53:10.204+0800: 171469.483: [GC[YG occupancy: 497152 K (943744 K)]2016-02-21T13:53:10.204+0800: 171469.483: [Rescan (parallel) , 1.3691900 secs]2016-02-21T13:53:11.573+0800: 171470.853: [weak refs processing, 0.1009300 secs]2016-02-21T13:53:11.674+0800: 1714
70.954: [class unloading, 0.0153470 secs]2016-02-21T13:53:11.689+0800: 171470.969: [scrub symbol table, 0.0110770 secs]2016-02-21T13:53:11.700+0800: 171470.980: [scrub string table, 0.0016360 secs] [1 CMS-remark: 1441609K(1560576K)] 1938761K(2504320K), 1.5079530 secs] [Ti
mes: user=13.01 sys=0.08, real=1.51 secs]
2016-02-21T13:53:11.712+0800: 171470.992: [CMS-concurrent-sweep-start]
{Heap before GC invocations=88668 (full 45):
 par new generation   total 943744K, used 914528K [0x0000000757000000, 0x0000000797000000, 0x0000000797000000)
  eden space 838912K, 100% used [0x0000000757000000, 0x000000078a340000, 0x000000078a340000)
  from space 104832K,  72% used [0x00000007909a0000, 0x0000000795378128, 0x0000000797000000)
  to   space 104832K,   0% used [0x000000078a340000, 0x000000078a340000, 0x00000007909a0000)
 concurrent mark-sweep generation total 1560576K, used 1441606K [0x0000000797000000, 0x00000007f6400000, 0x00000007f6400000)
 concurrent-mark-sweep perm gen total 159744K, used 78413K [0x00000007f6400000, 0x0000000800000000, 0x0000000800000000)
2016-02-21T13:53:11.775+0800: 171471.055: [GC2016-02-21T13:53:11.775+0800: 171471.055: [ParNew (promotion failed)
Desired survivor size 53673984 bytes, new threshold 6 (max 6)
- age   1:    4030872 bytes,    4030872 total
- age   2:    5959704 bytes,    9990576 total
- age   3:    4628680 bytes,   14619256 total
- age   4:    8773080 bytes,   23392336 total
- age   5:    7707144 bytes,   31099480 total
- age   6:   10890224 bytes,   41989704 total
: 914528K->907344K(943744K), 1.0312010 secs]2016-02-21T13:53:12.807+0800: 171472.086: [CMS2016-02-21T13:53:14.455+0800: 171473.735: [CMS-concurrent-sweep: 1.684/2.743 secs] [Times: user=3.69 sys=0.36, real=2.74 secs]
 (concurrent mode failure): 1451903K->475795K(1560576K), 3.9644230 secs] 2356134K->475795K(2504320K), [CMS Perm : 78413K->78413K(159744K)], 4.9959570 secs] [Times: user=5.65 sys=0.34, real=5.00 secs]
Heap after GC invocations=88669 (full 46):
 par new generation   total 943744K, used 0K [0x0000000757000000, 0x0000000797000000, 0x0000000797000000)
  eden space 838912K,   0% used [0x0000000757000000, 0x0000000757000000, 0x000000078a340000)
  from space 104832K,   0% used [0x000000078a340000, 0x000000078a340000, 0x00000007909a0000)
  to   space 104832K,   0% used [0x00000007909a0000, 0x00000007909a0000, 0x0000000797000000)
 concurrent mark-sweep generation total 1560576K, used 475795K [0x0000000797000000, 0x00000007f6400000, 0x00000007f6400000)
 concurrent-mark-sweep perm gen total 159744K, used 78413K [0x00000007f6400000, 0x0000000800000000, 0x0000000800000000)
}

• 在 CMS 启动过程中，新生代提升速度过快，老年代收集速度赶不上新生代提升速度
• 在 CMS 启动过程中，老年代碎片化严重，无法容纳新生代提升上来的大对象

• 新生代提升过快问题：（1）如果频率太快的话，说明空间不足，首先可以尝试调大新生代空间和晋升阈值。（2）如果内存有限，可以设置 CMS 垃圾收集在老年代占比达到多少时启动来减少问题发生频率（越早启动问题发生频率越低，但是会降低吞吐量，具体得多调整几次找到平衡点），参数如下：如果没有第二个参数，会随着 JVM 动态调节 CMS 启动时间

• 老年代碎片严重问题：（1）如果频率太快或者 Full GC 后空间释放不多的话，说明空间不足，首先可以尝试调大老年代空间（2）如果内存不足，可以设置进行 n 次 CMS 后进行一次压缩式 Full GC，参数如下：

2016-01-07T18:54:26.948+0800: 18782.967: [GC2016-04-07T18:54:26.948+0800: 18782.967: [ParNew (promotion failed)
Desired survivor size 117833728 bytes, new threshold 10 (max 10)
- age   1:    6141680 bytes,    6141680 total
- age   2:    6337936 bytes,   12479616 total
- age   3:     549120 bytes,   13028736 total
- age   4:      87768 bytes,   13116504 total
- age   5:     221384 bytes,   13337888 total
- age   6:     934168 bytes,   14272056 total
- age   7:     146072 bytes,   14418128 total
- age   8:     626064 bytes,   15044192 total
- age   9:     398000 bytes,   15442192 total
- age  10:     429616 bytes,   15871808 total
: 1969227K->1929200K(2071808K), 0.7452140 secs]2016-01-07T18:54:27.693+0800: 18783.713: [CMS: 1394703K->632845K(2097152K), 4.0993640 secs] 3301676K->632845K(4168960K), [CMS Perm : 77485K->77473K(159744K)], 4.8450240 secs] [Times: user=5.18 sys=0.56, real=4.84 secs]
Heap after GC invocations=5847 (full 7):
 par new generation   total 2071808K, used 0K [0x00000006e9c00000, 0x0000000776400000, 0x0000000776400000)
  eden space 1841664K,   0% used [0x00000006e9c00000, 0x00000006e9c00000, 0x000000075a280000)
  from space 230144K,   0% used [0x0000000768340000, 0x0000000768340000, 0x0000000776400000)
  to   space 230144K,   0% used [0x000000075a280000, 0x000000075a280000, 0x0000000768340000)
 concurrent mark-sweep generation total 2097152K, used 632845K [0x0000000776400000, 0x00000007f6400000, 0x00000007f6400000)
 concurrent-mark-sweep perm gen total 159744K, used 77473K [0x00000007f6400000, 0x0000000800000000, 0x0000000800000000)
}

• 新生代提升太快
• 老年代碎片太多，放不下大对象提升（表现为老年代还有很多空间但是，出现了 promotion failed）

{Heap before GC invocations=132 (full 0):
par new generation total 2696384K, used 2696384K [0xfffffffc20010000, 0xfffffffce0010000, 0xfffffffce0010000)
eden space 2247040K, 100% used [0xfffffffc20010000, 0xfffffffca9270000, 0xfffffffca9270000)
from space 449344K, 100% used [0xfffffffca9270000, 0xfffffffcc4940000, 0xfffffffcc4940000)
to space 449344K, 0% used [0xfffffffcc4940000, 0xfffffffcc4940000, 0xfffffffce0010000)
concurrent mark-sweep generation total 9437184K, used 1860619K [0xfffffffce0010000, 0xffffffff20010000, 0xffffffff20010000)
concurrent-mark-sweep perm gen total 1310720K, used 511451K [0xffffffff20010000, 0xffffffff70010000, 0xffffffff70010000)
2013-07-17T03:58:06.601-0700: 51522.120: [GC Before GC: : 2696384K->449344K(2696384K), 29.4779282 secs] 4557003K->2326821K(12133568K) ,29.4795222 secs] [Times: user=915.56 sys=6.35, real=29.48 secs]

• 详细的 GC 日志
• 借助 Linux 平台下的 iostat、vmstat、netstat、mpstat 等命令监控系统情况
• 使用 GCHisto 这个 GC 图形用户界面工具，可以统计出 Minor GC 及 Full GC 频率及时长分布，可参考:http://blog.csdn.net/wenniuwuren/article/details/50760259
• 查看 GC 日志中是否出现了上述的典型内存异常问题（promotion failed, concurrent mode failure），整体来说把上述两个典型内存异常情况控制在可接受的发生频率即可，对 CMS 碎片问题来说杜绝以上问题似乎不太可能，只能靠 G1 来解决了
• 是不是 JVM 本身的 bug 导致的
• 如果程序没问题，参数调了几次还是不能解决，可能说明流量太大，需要加机器把压力分散到更多 JVM 上

JVM 调优 —— GC 长时间停顿问题及解决方法

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原文地址：http://blog.csdn.net/wenniuwuren/article/details/51131741