OOM前排查

使用jmap导出当前堆dump进行离线分析

测试代码

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public class MyTest {

    private static List<String> list=new ArrayList<>();

    public static void main(String[] args) throws InterruptedException {
       for (int i=0;i<1000;i++){
           list.add("111");
       }
        TimeUnit.SECONDS.sleep(60);
    }

}

实时统计

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$ jmap -heap <pid>

导出dump

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$ jmap -dump:live,format=b,file=dump.hprof <pid>

然后使用jhat或者MAT进行分析

OOM后排查

配置jvm参数-XX:+HeapDumpOnOutOfMemoryError -Xmx1m

测试代码

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public class MyTest {

    private static List<String> list=new ArrayList<>();

    public static void main(String[] args) {
        while (true){
           list.add("111");
        }
    }

}

异常信息

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java.lang.OutOfMemoryError: Java heap space
Dumping heap to java_pid4352.hprof ...
Heap dump file created [1933323 bytes in 0.053 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:3210)
	at java.util.Arrays.copyOf(Arrays.java:3181)
	at java.util.ArrayList.grow(ArrayList.java:261)
	at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:235)
	at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:227)
	at java.util.ArrayList.add(ArrayList.java:458)
	at com.catfish.MyTest.main(MyTest.java:15)

可以看到jvm自动导出了java_pid4352.hprof

使用jhat分析

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$ jhat java_pid4352.hprof

Snapshot resolved.
Started HTTP server on port 7000
Server is ready.

可以通过访问 http://localhost:7000 来查看 dump 的数据

查看Show heap histogram

heap

参考资料

JDK内建工具