G1 issue: falling over to Full GC

[Vitaly Davidovich]

Hi Charlie,

Out of curiosity, is UseParallelOldGC advisable on, say, 6u23? It's off by
default, as you say, until 7u4 so I'm unsure if that's for some
good/specific reason or not.

Thanks

Sent from my phone
On Nov 2, 2012 8:36 AM, "Charlie Hunt" <chunt at salesforce.com> wrote:

> Jumping in a bit late ...
>
> Strongly suggest to anyone evaluating G1 to not use anything prior to 7u4.
>  And, even better if you use (as of this writing) 7u9, or the latest
> production Java 7 HotSpot VM.
>
> Fwiw, I'm really liking what I am seeing in 7u9 with the exception on one
> issue, (http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7143858),
> which is currently slated to be back ported to a future Java 7, (thanks
> Monica, John Cuthbertson and Bengt tackling this!).
>
> >From looking at your observations and others comments thus far, my
> initial reaction is that with a 1G Java heap, you might get the best
> results with -XX:+UseParallelOldGC.  Are you using -XX:+UseParallelGC, or
> -XX:+UseParallelOldGC?  Or, are you not setting a GC?  Not until 7u4 is
> -XX:+UseParallelOldGC automatically set for what's called "server class"
> machines when you don't specify a GC.
>
> The lengthy concurrent mark could be the result of the implementation of
> G1 in 6u*, or it could be that your system is swapping. Could you check if
> your system is swapping?  On Solaris you can monitor this using vmstat and
> observing, not only just free memory, but also sr == scan rate along with
> pi == page in and po == page out.  Seeing sr (page scan activity) along
> with low free memory along with pi & po activity are strong suggestions of
> swapping.  Seeing low free memory and no sr activity is ok, i.e. no
> swapping.
>
> Additionally, you are right.  "partial" was changed to "mixed" in the GC
> logs.  For those interested in a bit of history .... this change was made
> since we felt "partial" was misleading.  What partial was intended to mean
> was a partial old gen collection, which did occur.  But, on that same GC
> event it also included a young gen GC.  As a result, we changed the GC
> event name to "mixed" since that GC event was really a combination of both
> a young gen GC and portion of old gen GC.
>
> Simone also has a good suggestion with including -XX:+PrintFlagsFinal and
> -showversion as part of the GC log data to collect, especially with G1
> continuing to be improve and evolve.
>
> Look forward to seeing your GC logs!
>
> hths,
>
> charlie ....
>
> On Nov 2, 2012, at 5:46 AM, Andreas Müller wrote:
>
> > Hi Simone,
> >
> >> 4972.437: [GC pause (partial), 1.89505180 secs]
> >> that I cannot decypher (to Monica - what "partial" means ?), and no
> mixed GCs, which seems unusual as well.
> > Oops, I understand that now: 'partial' used to be what 'mixed' is now!
> > Our portal usually runs on Java 6u33. For the G1 tests I switched to 7u7
> because I had learned that G1 is far from mature in 6u33.
> > But automatic deployments can overwrite the start script and thus switch
> back to 6u33.
> >
> >> Are you sure you are actually using 1.7.0_u7 ?
> > I have checked that in the archived start scripts and the result,
> unfortunetaley, is: no.
> > The 'good case' was actually running on 7u7 (that's why it was good),
> but the 'bad case' was unwittingly run on 6u33 again.
> > That's the true reason why the results were so much worse and so
> incomprehensible.
> > Thank you very much for looking at the log and for asking good questions!
> >
> > I'll try to repeat the test and post the results on this list.
> >
> > Regards
> > Andreas
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