打印GC日志

最新推荐文章于 2025-01-16 16:39:24 发布

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1.在Arguments 设置 VM Arguments:-verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8

2.测试代码及日志打印
    public class MinorGCExample {

	private static final int _1MB=1024*1024;
	
	public static void testAllocation() {
		byte[] allocation1,allocation2,allocation3,allocation4;
		allocation1=new byte[2*_1MB];
		allocation2=new byte[2*_1MB];
		allocation3=new byte[2*_1MB];
		allocation4=new byte[4*_1MB];
	}
	public static void main(String[] args) {
		MinorGCExample.testAllocation();
	}
}

日志打印:
Heap
 PSYoungGen      total 9216K, used 7128K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 87% used [0x00000000ff600000,0x00000000ffcf6038,0x00000000ffe00000)
  from space 1024K, 0% used [0x00000000fff00000,0x00000000fff00000,0x0000000100000000)
  to   space 1024K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x00000000fff00000)
 ParOldGen       total 10240K, used 4096K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
  object space 10240K, 40% used [0x00000000fec00000,0x00000000ff000010,0x00000000ff600000)
 Metaspace       used 2647K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 285K, capacity 386K, committed 512K, reserved 1048576K

3.日志分析：对象优先在Eden分配

I.当新生对象在Eden区中分配。当Eden区没有足够空间进行分配时，虚拟机会进行一次Minor GC(新生代)

||.Arguments VM参数介绍:-XX:PrintGCDetails收集器日志参数，告诉虚拟机进行垃圾回收打印回收日志，程序退出时输出当前内存区域分配情况。

|||.testAllocation()方法中，尝试分配3个2MB大小和一个4MB大小，-Xms20M、-Xmx20M、-Xmn10M这三个参数限制了堆的大小不可扩展，新生代分配10M,剩余的10M分配给老年代。-XX:SurvivorRatio=8e决定了新生代中的Eden与Survivor区的空间比例为8：1