gc实例与gc报告的阅读

gc报告的浏览
首先我们看一条gc报告

D:\杂项\java>java -verbose:gc -Xms20m -Xmx20m -Xmn10m -XX:+PrintGCDetails  -XX:+UseSerialGC -XX:SurvivorRatio=8 testAllocation
[GC[DefNew: 7492K->980K(9216K), 0.0034913 secs] 7492K->7124K(19456K), 0.0037735 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]


Heap
 def new generation   total 9216K, used 3358K [0x00000000f9a00000, 0x00000000fa400000, 0x00000000fa400000)
  eden space 8192K,  29% used [0x00000000f9a00000, 0x00000000f9c52728, 0x00000000fa200000)
  from space 1024K,  95% used [0x00000000fa300000, 0x00000000fa3f5100, 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 2471K [0x00000000fae00000, 0x00000000fc2c0000, 0x0000000100000000)
   the space 21248K,  11% used [0x00000000fae00000, 0x00000000fb069d58, 0x00000000fb069e00, 0x00000000fc2c0000)
No shared spaces configured.D:\杂项\java>java -verbose:gc -Xm