解决CPU负载过高的Java应用程序的方式 [英] The way to solve cpu load too high of Java application

问题描述

今天，我发现我的服务器的CPU负载过高，服务器正在运行一个Java应用程序。

这是我的操作步骤。 / p>

1. 我使用 top 命令查找应用程序的pid。我使用 top -H -p 25713 命令来查找一些pid，它们是：pid = 25713。

使用了最多的CPU。如 25719 tomcat 20 0 10.6g 1.5g 13m R 97.8 4.7 314：35.22 java 。



2. 我使用 jstack -F 25713 命令打印转储信息，如Gang worker＃4（Parallel GC Threads）os_prio = 0 tid = 0x00007f5f10021800 nid = 0x6477 runnable




3. 我从转储文件中搜索了pid。然后我发现使用了大部分cpu的pids都像Gang worker＃4（Parallel GC Threads）os_prio = 0 tid = 0x00007f5f10021800 nid = 0x6477 runnable jstack 命令之后，cpu就变得正常了！

以下是我的问题：

1. 为什么 GC Threads 使cpu负载过高。


2. 为什么在我使用 jstack 命令后cpu成为正常。

超过这个时间，每次都是。 以下是一些正常的日志： 2015-10-10T10：17：52.019 + 0800：71128.973：[GC（分配失败）2015-10-10T10：17：52.019 + 0800：71128.973：[ParNew：309991K 206K（348416K），0.0051145秒] 616178K-> 306393K（1009920K），0.0052406秒] [时间：用户= 0.09 sys = 0.00，实际= 0.01秒]

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当CPU过高时，GC日志停留在 [GC（分配失败）2015-10-10T10：18：10.564 + 0800：71147.518：[ParNew ：，并且没有其他日志。

当我执行 jstack 命令时，打印日志

  2015-10-10T10：17：50.757 + 0800：53501.137：[GC（分配失败）2015-10 -10T10：17：50.757 + 0800：53501.137：[ParNew：210022K-> 245K（235968K），369.6907808secs] 400188K-> 1 
 90410K（1022400K），369.6909604sec] [Times：user = 3475.15 sys = 11.69，real = 369.63秒] 
  

解决方案

您可能会受 futex_wait错误影响 a>存在于某些内核版本中。

更一般地说， jstack -F 发送一个信号给进程，会中断任何可能正在睡觉的线程。所以也许GC线程只是旋转 - 等待另一个线程，不知何故错过了唤醒。即如果它确实停留在GC中并发送一个信号来修复问题，那么这可能指向锁或内存排序错误，如果不在内核中然后在JVM中。

不要使用 jstack -F ，你可以尝试发送 SIGBREAK 到这个过程，看看它是否有相同的效果。

Today, I found the cpu of load of my server is too high，and the server is just running a Java application.

Here are my operation steps.

1. I used top command to find the application's pid. The pid is 25713.

2. I used top -H -p 25713 command to find some pids which used the most of cpu. Such as 25719 tomcat 20 0 10.6g 1.5g 13m R 97.8 4.7 314:35.22 java.

3. I used jstack -F 25713 command to print the dump info.Such as "Gang worker#4 (Parallel GC Threads)" os_prio=0 tid=0x00007f5f10021800 nid=0x6477 runnable

4. I searched the pid from the dump file. Then I found that the pids which used most of cpu are all like "Gang worker#4 (Parallel GC Threads)" os_prio=0 tid=0x00007f5f10021800 nid=0x6477 runnable

5. After I used the jstack command, then the cpu became normal!

Here are my questions:

1. Why GC Threads made the cpu load too high.
2. Why after I used jstack command the cpu became nomal.

More than this time, every time.

Here are some normal logs.2015-10-10T10:17:52.019+0800: 71128.973: [GC (Allocation Failure) 2015-10-10T10:17:52.019+0800: 71128.973: [ParNew: 309991K->206K(348416K), 0.0051145 secs] 616178K->306393K(1009920K), 0.0052406 secs] [Times: user=0.09 sys=0.00, real=0.01 secs]

When the CPU comes too high, the GC log stay in [GC (Allocation Failure) 2015-10-10T10:18:10.564+0800: 71147.518: [ParNew:, and there is no other logs.

When I execute jstack command, the log printed

2015-10-10T10:17:50.757+0800: 53501.137: [GC (Allocation Failure) 2015-10-10T10:17:50.757+0800: 53501.137: [ParNew: 210022K->245K(235968K), 369.6907808 secs] 400188K->1
90410K(1022400K), 369.6909604 secs] [Times: user=3475.15 sys=11.69, real=369.63 secs] 

解决方案

Just guessing, you might be affected by the futex_wait bug present in certain kernel versions.

More generally, jstack -F sends a signal to the process, which will interrupt any thread that may be sleeping. So maybe GC threads just spin-waiting for another thread that somehow missed a wakeup. I.e. if it's indeed stuck in a GC and sending a signal fixes the problem then this may point to a locking or memory ordering bug, if not in the kernel then in the JVM.

Instead of using jstack -F you could try sending SIGBREAK to the process and see if that has the same effect.

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