ParallelGCThreads

[Y Srinivas Ramakrishna]

Hi Sujit --

> We have a distributed trading application. I have a processor set of 
> 16 CPU bound to process A and 8 CPU to process B. Please consider 
> following scenarios:
> 
> Scenario1: ParallelGCThreads set to 16 for both Process A and B.

16 for Process B is definitely the wrong setting. You should use
8 or less for Process B, since it has only an 8 processor pset to run on.

> 
> Scenario2: ParallelGCThreads set to 8 for both Process A and B.
> 
> Now for scenario2, I see that threadstop time has increased (got 
> worse) for process A and reduced (improved) for process B. Is this an 
> expected behaviour? Also will this (# of ParallelGCThreads vs # of 
> CPUs) impact rate of minor collections?

Yes, exactly as expected. In Scenario 2, you have more than 8 cpu's
available for GC of A, so using more than 8 GC threads is paying off.
If you exceed the # cpu's available, however, gc times will increase.
That's what you saw in the case of B going from Scenario 2 to Scenario 1.

#parallel gc threads does not affect the time between parallel collections,
but only the duration of the collections. The time between gcs is affected
(mainly) by the size of Eden and speed of the mutators.

-- ramki

> 
> Thanks and Regards,
> Sujit
> 
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