JVM参数配置

-XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=15 -Xms40M -Xmx40M -Xmn20M

新生代

• Eden 伊甸园
• survivor space0 幸存者，别称s0或from space
• survivor space1 幸存者，别称s1或to space

GC日志

JDK 1.6

堆描述

• def new generation 表示新生代
• tenured generation 表示老年代
• compacting perm gen 表示持久代

[GC [DefNew: 9031K->633K(18432K), 0.0026813 secs] 9031K->663K(38912K), 0.0027457 secs ]
[Times: user=0.00 sys=0.00, real=0.00 secs]

heap
def new generation total 18432K, used 9183K [0x241e0000, ...)
  eden space 16438K, 52% used [...)
  from space 2048K,  32% used [...)
  to   space 2048K,  0% used [...)

tenured generation total 20480K, used 0K [...)
  the space 20480K, 0% used [...)

compacting perm gen total 12288K, used 362K [...)
  the space 12288K, 2% used [...)
    ro space 8192K, 67% used [...)
    rw space 12288K, 53% used [...)

按照从前到后的顺序，依次解释：

JDK 1.7

堆描述

• PSYoungGen 表示新生代
• ParOldGen 表示老年代
• PSPermGen 表示持久代

Heap
 PSYoungGen      total 18432K, used 7791K [0x00000000fec00000, 0x0000000100000000, 0x0000000100000000)
  eden space 16384K, 47% used [0x00000000fec00000,0x00000000ff39bd78,0x00000000ffc00000)
  from space 2048K, 0% used [0x00000000ffe00000,0x00000000ffe00000,0x0000000100000000)
  to   space 2048K, 0% used [0x00000000ffc00000,0x00000000ffc00000,0x00000000ffe00000)

 ParOldGen       total 20480K, used 0K [0x00000000fd800000, 0x00000000fec00000, 0x00000000fec00000)
  object space 20480K, 0% used [0x00000000fd800000,0x00000000fd800000,0x00000000fec00000)

 PSPermGen       total 21504K, used 2584K [0x00000000f8600000, 0x00000000f9b00000, 0x00000000fd800000)
  object space 21504K, 12% used [0x00000000f8600000,0x00000000f8886080,0x00000000f9b00000)

按照从前到后的顺序，依次解释：