Where have the Full GCs gone?

Peter B. Kessler Peter.Kessler at Sun.COM
Wed Nov 5 00:52:20 UTC 2008


Moazam Raja wrote:
> Hi all, I'm running a test and recording GC information on a Tomcat  
> application and have noticed that even after a few days, there are no  
> 'Full GC' markers. Am I reading the log incorrectly, or are the Full  
> GCs getting logged elsewhere?
> 
> I'm using Java 1.5.0_13 on OS X with the following flags,
> 
>          -Xms=2048m -Xmx=2048m
>          -server -XX:+UseConcMarkSweepGC
>          -Xloggc:/var/tmp/GC.log
>          -verbose:gc
>          -XX:+PrintGCDetails
>          -XX:+PrintHeapAtGC
>          -XX:+PrintClassHistogram
>          -XX:+PrintGCApplicationConcurrentTime
> 
> 
> A sample of the output from my GC log:
> 
> 
> Application time: 1.4105823 seconds
> 82558.187: [GC {Heap before gc invocations=111716:
>   par new generation   total 21184K, used 21120K [0x0000000107270000, 0x0000000108730000, 0x0000000108730000)
>    eden space 21120K, 100% used [0x0000000107270000, 0x0000000108710000, 0x0000000108710000)
>    from space 64K,   0% used [0x0000000108710000, 0x0000000108710000, 0x0000000108720000)
>    to   space 64K,   0% used [0x0000000108720000, 0x0000000108720000, 0x0000000108730000)
>   concurrent mark-sweep generation total 20950272K, used 5483440K [0x0000000108730000, 0x0000000607270000, 0x0000000607270000)
>   concurrent-mark-sweep perm gen total 39296K, used 23575K [0x0000000607270000, 0x00000006098d0000, 0x000000060c670000)
> 82558.187: [ParNew: 21120K->0K(21184K), 0.0669633 secs] 5504560K->5487545K(20971456K)Heap after gc invocations=111717:
>   par new generation   total 21184K, used 0K [0x0000000107270000, 0x0000000108730000, 0x0000000108730000)
>    eden space 21120K,   0% used [0x0000000107270000, 0x0000000107270000, 0x0000000108710000)
>    from space 64K,   0% used [0x0000000108720000, 0x0000000108720000, 0x0000000108730000)
>    to   space 64K,   0% used [0x0000000108710000, 0x0000000108710000, 0x0000000108720000)
>   concurrent mark-sweep generation total 20950272K, used 5487545K [0x0000000108730000, 0x0000000607270000, 0x0000000607270000)
>   concurrent-mark-sweep perm gen total 39296K, used 23575K [0x0000000607270000, 0x00000006098d0000, 0x000000060c670000)
> }
> , 0.0672098 secs]
> ...

I don't think those are the command line arguments for the GC log you show.  It looks from the PrintHeapAtGG output that your heap is 20GB, not the 2GB shown on the command line.  20MB in the "par new" generation, and the reast of the 20GB in the CMS generation.

It looks like you are using just over 5GB of CMS space, which would explain why you haven't seen an old generation collection yet.

			... peter
_______________________________________________
hotspot-gc-use mailing list
hotspot-gc-use at openjdk.java.net
http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use



More information about the hotspot-gc-dev mailing list