PrintHeapAtGC and PrintTenuringDistribution

[Victor Cheung]

Hihi all,

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:

Application time: 0.7699290 seconds
{Heap before GC invocations=1 (full 0):
 PSYoungGen      total 305856K, used 73435K [0x00002aac78cb0000, 0x00002aac8e200000, 0x00002aad4e200000)
  eden space 262208K, 28% used [0x00002aac78cb0000,0x00002aac7d466ca8,0x00002aac88cc0000)
  from space 43648K, 0% used [0x00002aac8b760000,0x00002aac8b760000,0x00002aac8e200000)
  to   space 43648K, 0% used [0x00002aac88cc0000,0x00002aac88cc0000,0x00002aac8b760000)
 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)
2008-12-12T11:34:45.080-0500: 1.795: [GC
Desired survivor size 44695552 bytes, new threshold 7 (max 15)
 [PSYoungGen: 73435K->6960K(305856K)] 73435K->6960K(1004928K), 0.0088400 secs] [Times: user=0.04 sys=0.01, real=0.01 secs]
Heap after GC invocations=1 (full 0):
 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)
}
{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?

What does this mean?:  Desired survivor size 44695552 bytes, new threshold 7 (max 15)

Does it mean the desired *total* survivor space is 44MB (2 x 22 ss), or does it mean each of the two survivor spaces are 44MB?  What does the "threshold 7 (max 15)" mean?

Thanks,
victor

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