GC log question

What is the meaning of following (bold) in GC log:

81296.997: [GC 7431462K->6692307K(8283776K), 1.0975224 secs]

82337.956: [GC 7531219K->6800788K(8283776K), 1.1563326 secs]

83338.712: [GC 7639700K->6898225K(8283776K), 1.0868988 secs]

83339.816: [GC 6899724K(8283776K), 0.1227785 secs]

83351.437: [GC 6911811K(8283776K), 0.4253903 secs]

84363.941: [GC 1859011K->1125589K(8283776K), 0.9137798 s开发者_JS百科ecs]

85319.780: [GC 1964501K->1217720K(8283776K), 0.8500309 secs]

I expect a Full in log after around 95% of my Xmx but what I see is above. My settings are below:

-d64  
-Xss384k  
-Xms8192m
-Xmx8192m  
-XX:ParallelGCThreads=12  
-XX:PermSize=512m  
-XX:MaxPermSize=512m  
-XX:NewSize=1024m  
-XX:MaxNewSize=1024m  
-XX:SurvivorRatio=8  
-Xnoclassgc  
-XX:+DisableExplicitGC  
-verbose:gc  
-XX:+UseParNewGC  
-XX:+CMSParallelRemarkEnabled  
-XX:+UseConcMarkSweepGC

Let me rephrase my question: I know what the meaning of the entire line but my question was why the bold lines are different and what kind of GC it is? I dont think it is a Young Generation GC, if not then what kind of GC is this?

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This looks weird. The lines in bold definitely seem to belong to a young generation GC. It also appears from the fact that no space was freed up and from the short time they took that they were failed attempts, which could have happened because there wasn't enough space in the old generation to tenure all the objects that needed to be.

What I find weird is the next line though:

84363.941: [GC 1859011K->1125589K(8283776K), 0.9137798 secs]

What happened in between that made three quarters of the memory free up? It could be an anomaly caused by the logging of parralel GC but something's not right there.

You could try adding -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintTenuringDistribution to get a clearer view. (In conjunction with the -Xloggc:<log file> option of course.)

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I am not very sure, but seems like the number outside bracket is the timestamp, the number after 'GC' is the memory after GC and the one in bracket is the number before GC happened. The rest is intuitive.