PrintHeapAtGC and PrintTenuringDistribution

Y Srinivas Ramakrishna Y.S.Ramakrishna at Sun.COM
Fri Dec 12 10:33:52 PST 2008


> I was able to (finally) get admin to add some options to the JBoss 
> start script on staging and I'm trying to understand the output.  I 
> have a couple of questions about the following snippet:
> 

...
> {Heap before GC invocations=2 (full 1):
>  PSYoungGen      total 305856K, used 6960K [0x00002aac78cb0000, 
> 0x00002aac8e200000, 0x00002aad4e200000)
>   eden space 262208K, 0% used [0x00002aac78cb0000,0x00002aac78cb0000,0x00002aac88cc0000)
>   from space 43648K, 15% used [0x00002aac88cc0000,0x00002aac8938c140,0x00002aac8b760000)
>   to   space 43648K, 0% used [0x00002aac8b760000,0x00002aac8b760000,0x00002aac8e200000)
>  PSOldGen        total 699072K, used 0K [0x00002aaace200000, 
> 0x00002aaaf8cb0000, 0x00002aac78cb0000)
>   object space 699072K, 0% used [0x00002aaace200000,0x00002aaace200000,0x00002aaaf8cb0000)
>  PSPermGen       total 524288K, used 17851K [0x00002aaaae200000, 
> 0x00002aaace200000, 0x00002aaace200000)
>   object space 524288K, 3% used [0x00002aaaae200000,0x00002aaaaf36efe0,0x00002aaace200000)
> 2008-12-12T11:34:45.089-0500: 1.803: [Full GC (System) [PSYoungGen: 
> 6960K->0K(305856K)] [PSOldGen: 0K->6684K(699072K)] 
> 6960K->6684K(1004928K) [PSPermGen: 17
> 851K->17851K(524288K)], 0.0631930 secs] [Times: user=0.06 sys=0.01, 
> real=0.06 secs]
> Heap after GC invocations=2 (full 1):
>  PSYoungGen      total 305856K, used 0K [0x00002aac78cb0000, 
> 0x00002aac8e200000, 0x00002aad4e200000)
>   eden space 262208K, 0% used [0x00002aac78cb0000,0x00002aac78cb0000,0x00002aac88cc0000)
>   from space 43648K, 0% used [0x00002aac88cc0000,0x00002aac88cc0000,0x00002aac8b760000)
>   to   space 43648K, 0% used [0x00002aac8b760000,0x00002aac8b760000,0x00002aac8e200000)
>  PSOldGen        total 699072K, used 6684K [0x00002aaace200000, 
> 0x00002aaaf8cb0000, 0x00002aac78cb0000)
>   object space 699072K, 0% used [0x00002aaace200000,0x00002aaace8870f8,0x00002aaaf8cb0000)
>  PSPermGen       total 524288K, used 17851K [0x00002aaaae200000, 
> 0x00002aaace200000, 0x00002aaace200000)
>   object space 524288K, 3% used [0x00002aaaae200000,0x00002aaaaf36efe0,0x00002aaace200000)
> }
> Total time for which application threads were stopped: 0.0728370 seconds
> Application time: 0.3355980 seconds
> Total time for which application threads were stopped: 0.0006860 seconds
> Application time: 0.0913380 seconds
> 
> 
> 
> When exactly did the Full GC occur?  Was it GC invocation #1, or GC 
> invocation #2?

It was GC invocation#2 which was also Full GC invocation#1 (note the two
different counts displayed -- the first is the total invocations of
all gc's, major or minor; the second is the total invocations of
full/major gc). It started at start+1.803 seconds and took about 63 ms.
It was the result of a System.gc() invocation.

Jon already answered yr other questions (elided).
-- ramki
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