G1gc compaction algorithm

[Martin Makundi]

> > +PrintHeapAtGC -XX:+PrintHeapAtGCExtended .

Does it print only on Full GC or any GC? Any gc might be an overkill.

>  You want that probably:
> https://bugs.openjdk.java.net/browse/JDK-8038487

I cannot comment (didn't find a way to register as user) on that entry but
you could add a comment on my behalf that   "continuous parallel
compaction"  would be nice.

**
Martin



2014-07-16 9:51 GMT+03:00 Thomas Schatzl <thomas.schatzl at oracle.com>:

> Hi,
>
> On Wed, 2014-07-16 at 09:41 +0300, Martin Makundi wrote:
> > Hi!
> >
> > I am not sure what's my issue, but according to logs the humongous
> > object size varies... usually it's the larger ones that hit the fan
> > unless the region size is too large to start with. I tried 16m and it
> > seemed to make itworse, tried couple more values here and there and 5M
> > seems to work quite nicely.
>
> 4M I guess (it does not matter).
> >
> > I suspect it's fragmentation issue, because most often Full GC occurs
> > at 60-70% total heap used while the humongous object size is only 0,1%
> > of the total heap size.
> >
> >
> > So I suspect something like "continuous parallel compaction" could
> > solve my issue?
>
> You want that probably:
> https://bugs.openjdk.java.net/browse/JDK-8038487
> >
> > > You can get current region distribution information by eg. -XX:
> > > +PrintHeapAtGC -XX:+PrintHeapAtGCExtended .
> >
> > First one I had already, will add latter one. What will these look
> > like on the logs, i.e., how can I search for them and look at the
> > particular output?
> >
> At the end of GC it prints for what purpose the regions are used
> currently per region. One region per line, so it fills up your logs.
>
> However using it you can see if the humongous allocation request of a
> particular size could actually fit or not. The described behavior fits
> the typical symptoms for that issue.
>
> Thanks,
> Thomas
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/hotspot-gc-use/attachments/20140716/1695f51b/attachment.html>