打印gc.log 观察gc情况

在catalina.sh加入
-XX:+PrintClassHistogram -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -Xloggc:log/gc.log（具体位置应该都知道，set java_opts那里）

可以在/home/log下生产一个gc.log的文件
可以将此文件sz下来或者直接tail观看gc的情况。

以下是我gc.log中的一个片段

{Heap before GC invocations=1 (full 0):
PSYoungGen total 917504K, used 31458K [0x00000007c0000000, 0x0000000800000000, 0x0000000800000000)
eden space 786432K, 4% used [0x00000007c0000000,0x00000007c1eb8858,0x00000007f0000000)
from space 131072K, 0% used [0x00000007f8000000,0x00000007f8000000,0x0000000800000000)
to space 131072K, 0% used [0x00000007f0000000,0x00000007f0000000,0x00000007f8000000)
ParOldGen total 1048576K, used 0K [0x0000000700000000, 0x0000000740000000, 0x00000007c0000000)
object space 1048576K, 0% used [0x0000000700000000,0x0000000700000000,0x0000000740000000)
PSPermGen total 131072K, used 10488K [0x00000006f0000000, 0x00000006f8000000, 0x0000000700000000)
object space 131072K, 8% used [0x00000006f0000000,0x00000006f0a3e3a8,0x00000006f8000000)
0.793: [GC [PSYoungGen: 31458K->4293K(917504K)] 31458K->4301K(1966080K), 0.0087090 secs] [Times: user=0.03 sys=0.00, real=0.01 secs]
Heap after GC invocations=1 (full 0):
PSYoungGen total 917504K, used 4293K [0x00000007c0000000, 0x0000000800000000, 0x0000000800000000)
eden space 786432K, 0% used [0x00000007c0000000,0x00000007c0000000,0x00000007f0000000)
from space 131072K, 3% used [0x00000007f0000000,0x00000007f04316a0,0x00000007f8000000)
to space 131072K, 0% used [0x00000007f8000000,0x00000007f8000000,0x0000000800000000)
ParOldGen total 1048576K, used 8K [0x0000000700000000, 0x0000000740000000, 0x00000007c0000000)
object space 1048576K, 0% used [0x0000000700000000,0x0000000700002000,0x0000000740000000)
PSPermGen total 131072K, used 10488K [0x00000006f0000000, 0x00000006f8000000, 0x0000000700000000)
object space 131072K, 8% used [0x00000006f0000000,0x00000006f0a3e3a8,0x00000006f8000000)
}

ps：附上一张gc log的解释图