jvm MinorGC和查看GC日志

【代码】

public class Page93 {
	private static final int _1MB = 1024 * 1024;
	
	public static void main(String[] args) {
		
		minorGC(); 
	}
	
	/**
	 * vm params: -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8
	 */
	private static void minorGC() {

		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]; 
	}
}

// 运行结果，打印gc日志
D:\bench-cluster\spring_in_action_eclipse\jvm\src>java -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 chapter3.Page93
Heap
 PSYoungGen      total 9216K, used 7300K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
  eden space 8192K, 89% used [0x00000000ff600000,0x00000000ffd210f0,0x00000000ffe00000)
  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 2550K, capacity 4486K, committed 4864K, reserved 1056768K
  class space    used 279K, capacity 386K, committed 512K, reserved 1048576K

有个问题是，Metaspace 是个什么玩意儿啦？

Metaspace 是java8用来替代持久代的产物；参见 

https://www.cnblogs.com/xrq730/p/8688203.html