G1gc compaction algorithm

[yao]

Hi Martin,

I think you may mean do a normal GC when you say "compacting",  then that's
exactly what this JIRA talk about. If you really mean do a cross region
compacting (combing live objects from several regions to a single one), I
don't think this is implemented so far, at least in jvm 7. Even that was
implemented, if your heap has free regions, I think compacting doesn't
really matter. In addition, there are several G1 parameters you can tune to
prevent scattered regions (regions with few live objects), see
http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html. Without
seeing the full gc log, I cannot say much how to tune G1 for your case but
I would definitely try reducing XX:G1HeapWastePercent first.

Best
Shengzhe


On Wed, Jul 16, 2014 at 12:11 AM, Martin Makundi <
martin.makundi at koodaripalvelut.com> wrote:

>
>> On Wed, 2014-07-16 at 10:02 +0300, Martin Makundi wrote:
>> > > > +PrintHeapAtGC -XX:+PrintHeapAtGCExtended .
>> >
>> > Does it print only on Full GC or any GC? Any gc might be an overkill.
>>
>> Unfortunately any GC :/
>>
>> >
>> > >  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.
>>
>> I can add a comment, but what do you mean with "continuous parallel
>> compaction" if I may ask, and what exact purpose does it serve?
>>
>> The terms are too generic to me to discern any particular functionality.
>>
>
> I mean that currently compacting occurs on full gc meaning stop-the-world.
> Would be nice if compacting would occur in parallel while app is running
> and taking into account all timing targets such as MaxGCPauseMillis etc.
>
> **
> Martin
>
>>
>> Thanks,
>>   Thomas
>>
>>
>>
>
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