一、问题:
春节将至,系统访问量进入高峰期。随之系统出现了异常:java.lang.OutOfMemoryError: unable to create new native thread。在解决这个问题中,尝试了各种方法,最后竟然是因为它......
二、解决办法:
1、 关于这个问题,一开始猜想是因消息队列(activemq)引起的,因为处理数据较多,开启的线程数较多导致,因此对MQ搭建了集群。
MQ集群搭建方法:http://blog.****.net/jiangxuchen/article/details/8004561
但是搭建集群后发现,并没有什么卵用,问题依旧。
继续......
2、 接下来怀疑是系统里开的线程数太多,在优化后,问题仍然存在。
继续......
3、 内存调优,减小xss值、JVM内存,仍然解决不了。
继续......
4、 几番周测,在整理思路后,决定首要任务就是如何重现该问题,于是编写测试程序,测试出操作系统最大能够创建的线程数:
import java.util.concurrent.CountDownLatch; public class TestNativeOutOfMemoryError { public static void main(String[] args) { for (int i = 0;; i++) {
System.out.println("i = " + i);
new Thread(new HoldThread()).start();
}
} } class HoldThread extends Thread {
CountDownLatch cdl = new CountDownLatch(1); public HoldThread() {
this.setDaemon(true);
} public void run() {
try {
cdl.await();
} catch (InterruptedException e) {
}
}
}
运行后:
i = 982
Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:597)
at TestNativeOutOfMemoryError.main(TestNativeOutOfMemoryError.java:20)
问题重现,在反复运行几次后发现,生产系统最大只能创建980多个线程,生产系统操作系统64位centeros,jdk1.7,64G内存。而我本地PC电脑都可以创建2500左右。
感觉原因快找到了,切换到运行账户使用命令:
$ su Bst118
$ ulimit -u
$ 1024
生产上所有程序都是在Bst118账户下运行,于是查看该账户下所有的线程数总和为950,也即是说,随时都可能会超过1024,导致内存溢出。查看看进程当前运行的线程数命令为:pstree -p 3660 | wc -l
原因找到,操作系统对运行程序的账户有最大线程数限制。
$ vim /etc/security/limits.d/90-nproc.conf
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打开后发现除了root,其他账户都限制在1024个。
于是增加一条:Bst118 soft nproc 20000
为什么设置为20000,因为测试后发现,在运行到35000左右,系统就报内存溢出了,操作系统所有命令都不能使用,因此将程序最大线程数限制在20000。
修改后再没出现内存溢出错误。问题解决。
三、思考
1、经过总结,在遇到问题后,不能盲目的到处修改,首先要做的就是重现问题,顺藤摸瓜,逐步的找出根本原因。
2、关于tomcat内存调优,个人认为只有在中大型系统才需要调优或者服务器硬件条件一般的情况下才需要调优,才能有所效果。