JVM探索（一）

JVM测试的样例代码：

import java.lang.management.ManagementFactory;

/**

 * @author zhailzh

 * 

 * @Date 2015年10月31日——下午14:18:15

 * 

 */

public class Main {

  private static final int _1m = 1024 * 1024;

  public static void main(String[]  (full 0):

par new generation total 9216K, used 7145K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000)

eden space 8192K, 87% used [0x00000000f9a00000, 0x00000000fa0fa540, 0x00000000fa200000)

from space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000)

to space 1024K, 0% used [0x00000000fa300000, 0x00000000fa300000, 0x00000000fa400000)

tenured generation total 10240K, used 0K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000)

the space 10240K, 0% used [0x00000000fa400000, 0x00000000fa400000, 0x00000000fa400200, 0x00000000fae00000)

compacting perm gen total 21248K, used 2792K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000)

the space 21248K, 13% used [0x00000000fae00000, 0x00000000fb0ba1d0, 0x00000000fb0ba200, 0x00000000fc2c0000)

No shared spaces configured.

Heap after GC invocations=1 (full 0):

par new generation total 9216K, used 541K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000)

eden space 8192K, 0% used [0x00000000f9a00000, 0x00000000f9a00000, 0x00000000fa200000)

from space 1024K, 52% used [0x00000000fa300000, 0x00000000fa387788, 0x00000000fa400000)

to space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000)

tenured generation total 10240K, used 6144K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000)

the space 10240K, 60% used [0x00000000fa400000, 0x00000000faa00030, 0x00000000faa00200, 0x00000000fae00000)

compacting perm gen total 21248K, used 2792K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000)

the space 21248K, 13% used [0x00000000fae00000, 0x00000000fb0ba1d0, 0x00000000fb0ba200, 0x00000000fc2c0000)

No shared spaces configured.

}

jstat监测：

首先对jstat上面的指标进行介绍：S0、S1 代表的是幸存1区，幸存2区或者叫做from或者to区。E 代表伊甸区，P代表老年代，

YGC垃圾回收的次数，T代表时间，FGC代表full gc。c 代表总量， u代表使用量。那么S0C表示幸存1区

的总容量为512M，S0U表示幸存1区使用了0M，EC表示伊甸区的容量，OU老年代的使用的量。

那我们来分析输出的日志：

第一行：% used [0x00000000f9a00000, 0x00000000fa0fa540, 0x00000000fa200000)

from space 1024K, 0% used [0x00000000fa200000, 0x00000000fa200000, 0x00000000fa300000)

to space 1024K, 0% used [0x00000000fa300000, 0x00000000fa300000, 0x00000000fa400000)

tenured generation total 10240K, used 0K [0x00000000fa400000, 0x00000000fae00000, 0x00000000fae00000)

the space 10240K, 0% used [0x00000000fa400000, 0x00000000fa400000, 0x00000000fa400200, 0x00000000fae00000)

compacting perm gen total 21248K, used 2792K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000)

the space 21248K, 13% used [0x00000000fae00000, 0x00000000fb0ba1d0, 0x00000000fb0ba200, 0x00000000fc2c0000)