Question

我正在经历使用G1GC算法的罕见长GC暂停 - 一个月超过30秒。一旦发生这种情况，我会重新启动我的服务，这种延迟将在接下来的一个月内再次发生。

我正在附加GC日志。

2016-06-15T02:30:17.407-0400: 1702455.276: Total time for which application threads were stopped: 0.2900480 seconds
2016-06-15T02:30:25.509-0400: 1702463.378: Total time for which application threads were stopped: 0.0018900 seconds
2016-06-15T02:30:29.817-0400: 1702467.686: [GC pause (young)
Desired survivor size 7340032 bytes, new threshold 15 (max 15)
- age   1:    1903912 bytes,    1903912 total
- age   2:     641440 bytes,    2545352 total
- age   3:     455856 bytes,    3001208 total
- age   4:     563544 bytes,    3564752 total
- age   5:    1873368 bytes,    5438120 total
- age   6:     326024 bytes,    5764144 total
- age   7:     299144 bytes,    6063288 total
- age   8:     304632 bytes,    6367920 total
- age   9:     273160 bytes,    6641080 total
- age  10:     309152 bytes,    6950232 total
- age  11:     156824 bytes,    7107056 total
- age  12:     135064 bytes,    7242120 total
, 0.1199490 secs]
   [Parallel Time: 118.2 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 1702467686.7, Avg: 1702467686.8, Max: 1702467686.9, Diff: 0.2]
      [Ext Root Scanning (ms): Min: 18.4, Avg: 20.2, Max: 24.6, Diff: 6.2, Sum: 80.7]
      [Update RS (ms): Min: 75.5, Avg: 79.5, Max: 80.8, Diff: 5.3, Sum: 317.8]
         [Processed Buffers: Min: 52, Avg: 61.0, Max: 70, Diff: 18, Sum: 244]
      [Scan RS (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.3]
      [Object Copy (ms): Min: 17.7, Avg: 18.1, Max: 18.6, Diff: 0.8, Sum: 72.3]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [GC Worker Other (ms): Min: 0.1, Avg: 0.1, Max: 0.1, Diff: 0.0, Sum: 0.4]
      [GC Worker Total (ms): Min: 117.8, Avg: 117.9, Max: 118.0, Diff: 0.2, Sum: 471.6]
      [GC Worker End (ms): Min: 1702467804.7, Avg: 1702467804.7, Max: 1702467804.7, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Clear CT: 0.2 ms]
   [Other: 1.6 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.3 ms]
      [Ref Enq: 0.0 ms]
      [Free CSet: 0.4 ms]
   [Eden: 100.0M(100.0M)->0.0B(100.0M) Survivors: 9216.0K->9216.0K Heap: 2164.6M(2198.0M)->2065.5M(2198.0M)]
 [Times: user=0.48 sys=0.00, real=37.62 secs]
2016-06-15T02:31:07.438-0400: 1702505.307: Total time for which application threads were stopped: 37.6223210 seconds

2016-06-15T02:31:07.443-0400: 1702505.312: Total time for which application threads were stopped: 0.0034690 seconds
2016-06-15T02:31:07.446-0400: 1702505.315: Total time for which application threads were stopped: 0.0018140 seconds
2016-06-15T02:31:07.451-0400: 1702505.320: Total time for which application threads were stopped: 0.0020130 seconds
2016-06-15T02:31:07.453-0400: 1702505.322: Total time for which application threads were stopped: 0.0015850 seconds

我在G1GC标志下面使用：

-server -d64 -verbose:gc -Xms2g -Xmx4g -XX:+UseG1GC 
-XX:MaxGCPauseMillis=1500 -XX:G1HeapRegionSize=2 
-XX:+PrintFlagsFinal -XX:ParallelGCThreads=4 -XX:ConcGCThreads=2 
-XX:PermSize=64m -XX:MaxPermSize=256m -XX:+DisableExplicitGC 
-XX:+PrintGCDateStamps -XX:+DoEscapeAnalysis -XX:+PrintTenuringDistribution 
-XX:+PrintGCTimeStamps -XX:+PrintGCDetails 
-XX:+PrintGCApplicationStoppedTime -XX:+HeapDumpOnOutOfMemoryError 
-XX:HeapDumpPath=$PP_HOME -XX:+UseCompressedOops -XX:+AggressiveOpts"

机器配置：

Red Hat Enterprise Linux Server release 5.11 
Dual core CPU
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

我们怎样才能从上述陈述中找到长GC的根本原因？

Answer 1

更新到最新版本的Java 8 - 您应该不将G1与Java 7一起使用，因为那时它还没有准备就绪。很有可能你已经遇到了一个现已修补过的bug。是的，有方式将OpenJDK 8放到RHEL 5盒子上。是的，您的申请将在速度上大幅提升。

另外，这个：

-XX：MaxGCPauseMillis = 1500

和此：

-Xms2g -Xmx4g

建议你不要在大堆，低延迟环境G1中运行。使用旧的JRE，您可能会更好地使用默认（ParallelGC）和可能调整一些选项以减少暂停时间（里程可能会有所不同）。或者CMS，它更成熟，然后调整可以非常稳定。

为了善良，如果你的应用足够严重，每个月30秒的GC暂停是一个问题，那么你可能买得起RHEL 7和超过双核的系统。

不经常长的GC暂停与G1GC

1 个答案: