G1GC Full GCs

Todd Lipcon todd at cloudera.com
Fri Jul 30 14:11:52 PDT 2010

On Fri, Jul 30, 2010 at 1:56 PM, Peter Schuller <peter.schuller at infidyne.com
> wrote:

> > I consistently am seeing "Other time" estimates in the >40ms range. Given
> my
> > pause time goal of 20ms, these estimates are I think excluding most of
> the
> Btw, to test the hypothesis: When you say "constantly", are the times
> in fact so consistent that it's either exactly the same or almost,
> possibly being consistent with my proposed hypothesis that the
> non-young "other" time is stuck? If the young other time is not stuck
> I guess one might see some variation (I seem to get < 1 ms on my
> machine) but not a lot at all in comparison to 40ms. If you're seeing
> variation like 40-42 all the time, and it never decreasing
> significantly after it reached the 40ms range, that would be
> consistent with the hypothesis I believe.
Hi Peter,

There shouldn't be any swapping during the tests - I've got RAM fairly
carefully allocated and I believe swappiness was tuned down on those
machines, though I will double check to be certain.

I'll try to read through your full email in detail while looking at the
source and the G1 paper -- right now it's a bit above my head :)

FWIW, my tests on JRockit JRRT's gcprio:deterministic collector didn't go
much better - eventually it fell back to a full compaction which lasted 45
seconds or so. HBase must be doing something that's really hard for GCs to
deal with - either on the heuristics front or on the allocation pattern


Todd Lipcon
Software Engineer, Cloudera
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