GC 和 OOM 举例

柔情只为你懂 2021-07-24 15:23 387阅读 0赞

# 一 代码 #

import java.util.ArrayList;
    import java.util.List;
    
    /**
    * 测试 MinorGC、MajorGC、FullGC
    * -Xms9m -Xmx9m -XX:+PrintGCDetails
    */
    public class GCTest {
        public static void main(String[] args) {
            int i = 0;
            try {
                List<String> list = new ArrayList<>();
                String a = "cakin";
                while (true) {
                    list.add(a);
                    a = a + a;
                    i++;
                }
            } catch (Throwable t) {
                t.printStackTrace();
                System.out.println("遍历次数为：" + i);
            }
        }
    }

# 二 测试 #

[GC (Allocation Failure) [PSYoungGen: 2048K->488K(2560K)] 2048K->961K(9728K), 0.0028277 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
    [GC (Allocation Failure) [PSYoungGen: 2393K->500K(2560K)] 2866K->1674K(9728K), 0.0013144 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
    [GC (Allocation Failure) [PSYoungGen: 2153K->444K(2560K)] 3327K->2258K(9728K), 0.0008944 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
    [Full GC (Ergonomics) [PSYoungGen: 2457K->0K(2560K)] [ParOldGen: 6934K->5886K(7168K)] 9391K->5886K(9728K), [Metaspace: 3250K->3250K(1056768K)], 0.0084179 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
    [GC (Allocation Failure) [PSYoungGen: 0K->0K(2560K)] 5886K->5886K(9728K), 0.0003287 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
    [Full GC (Allocation Failure) [PSYoungGen: 0K->0K(2560K)] [ParOldGen: 5886K->5866K(7168K)] 5886K->5866K(9728K), [Metaspace: 3250K->3250K(1056768K)], 0.0076788 secs] [Times: user=0.05 sys=0.00, real=0.01 secs]
    遍历次数为：17
    Heap
    PSYoungGen      total 2560K, used 93K [0x00000000ffd00000, 0x0000000100000000, 0x0000000100000000)
      eden space 2048K, 4% used [0x00000000ffd00000,0x00000000ffd17790,0x00000000fff00000)
      from space 512K, 0% used [0x00000000fff80000,0x00000000fff80000,0x0000000100000000)
      to   space 512K, 0% used [0x00000000fff00000,0x00000000fff00000,0x00000000fff80000)
    ParOldGen       total 7168K, used 5866K [0x00000000ff600000, 0x00000000ffd00000, 0x00000000ffd00000)
      object space 7168K, 81% used [0x00000000ff600000,0x00000000ffbbab08,0x00000000ffd00000)
    Metaspace       used 3295K, capacity 4496K, committed 4864K, reserved 1056768K
      class space    used 356K, capacity 388K, committed 512K, reserved 1048576K
    java.lang.OutOfMemoryError: Java heap space
        at java.util.Arrays.copyOfRange(Arrays.java:3664)
        at java.lang.String.<init>(String.java:207)
        at java.lang.StringBuilder.toString(StringBuilder.java:407)
        at com.atguigu.java.chapter08.java1.GCTest.main(GCTest.java:18)

# 三 说明 #

1 触发 OOM 的时候，一定是进行了一次Full GC。

2 只有在老年代空间不足时候，才会产生 OOM 异常。

3 打印解读

> Full GC (Ergonomics)：发生了一次Full GC。 
> 
> \[PSYoungGen: 2457K->0K(2560K)\] ：Full GC 前后，新生代内存变化情况。
> 
> \[ParOldGen: 6934K->5886K(7168K)\] ：Full GC 前后，老年代内存变化情况。
> 
> 9391K->5886K(9728K)：Full GC 前后，整个堆内存变化情况
> 
> \[Metaspace: 3250K->3250K(1056768K)\]：Full GC 前后，元空间内存变化情况。