java-Performance Tuning-Understanding GC Logs

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[ ~]# cat gc.log.0 | grep ‘Full GC‘1.652: [Full GC (System) 1.652: [CMS: 0K->21718K(262144K), 0.0837910 secs] 48398K->21718K(458752K), [CMS Perm : 16462K->16457K(21248K)], 0.0841650 secs] [Times: user=0.08 sys=0.00, real=0.08 secs] 664643.879: [GC 664643.879: [ParNew: 134434K->3202K(196608K), 0.0068030 secs] 327839K->196659K(458752K) icms_dc=0 , 0.0070080 secs] [Times: user=0.03 sys=0.00, real=0.01 secs]

1.625, 664643.879 is the time that the GC occurred, the number of seconds elapsed since the Java Virtual machine was started.

"[GC" and "[Full GC" indicate the type of GC pauses, rather than distinguishing between the Cenozoic GC and the old-age GC.

The full GC will occur Stop-the-world (STW). If the full GC triggered by System.GC () is called, "[Full GC (System)" is displayed

[Defnew, [tenured, [perm indicates the area where GC occurs:

[Defnew:serial Collector in the Cenozoic

[Parnew:parnew collector Cenozoic

[Psyounggen:parallel scanvenge collector Cenozoic

[Cms:cms collector old age

[Tenured:serial collector old age

[Perm,[cms Perm: Permanent generation

1	134434K->3202K(196608K) 含义： “GC前内存区已使用容量->GC后内存区已使用容量（该内存区域总容量）”

1	[Times: user=0.03sys=0.00, real=0.01secs] 含义：user,sys,real分别表示用户消耗CPU时间、内核消耗CPU时间、操作从开始到结束所经过的墙钟时间（wall clock time）<br>CPU时间与墙钟时间的区别：墙钟时间包括各种非运算等待时间，如IO阻塞等待，而CPU不包括这些时间。

java-Performance Tuning-Understanding GC Logs