Where have the Full GCs gone?

[Moazam Raja]

Peter, this must be a bug in the GC output as I know for sure I don't  
have the memory to run a 20GB heap.

Instead of 20950272K, it must mean 20950272Kb.

This is on Java 1.5.0 on OS X Leopard.

java version "1.5.0_13"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_13- 
b05-237)
Java HotSpot(TM) Server VM (build 1.5.0_13-119, mixed mode)


-Moazam

On Nov 4, 2008, at 4:52 PM, Peter B. Kessler wrote:

> 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

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