G1GC fine tuning under heavy load
Stefan Johansson
stefan.johansson at oracle.com
Fri Sep 14 08:55:41 UTC 2018
Thanks for the log,
After looking through the log I think the suggestion to increase
InitiatingHeapOccupancyPercent (IHOP) stands. Your old generation is
growing slowly and after a while it gets above the concurrent cycle
threshold which is 45% of the heap (~ 3225M for a 7G heap). When the
concurrent cycle finishes and the Mixed collections try to reclaim old
generation space only a few megabytes is reclaimed before the ergonomics
decide to not do more Mixed collections. The reason for this is that
most of the old generation data is still live, roughly 90%. If you want
the Mixed collection to reclaim some more space you can lower the
G1HeapWastePercent value, which by default is 5. This will generate a
few more Mixed collections that can reclaim some additional space, and
it might be worth it since some much in old is live.
If you raise the IHOP a bit you should be able to avoid the back to back
concurrent cycles and also be able to reclaim some more space when the
Mixed collections are actually running.
One thing that you should investigate is why the old generation is
growing over time, if this is expected you will run into the same
problem later on when it has grown to the new IHOP value.
One additional point, if you have the possibility I would suggest trying
to run with a later version of Java, there have been some great
improvements done to G1 and the feature adaptive IHOP could very well
help you to avoid doing this kind of tuning.
Hope this helps,
Stefan
On 2018-09-13 23:34, Wajih Ahmed wrote:
> The link to the file is
> https://drive.google.com/open?id=1Y8ZvxxHy078xPjJFy26nMhxeTaWgIcwn. And
> i hope i have the correct file corresponding to the report but even if
> it is not it will exhibit the same pattern as it could be from one of
> the servers in the cluster.
>
> Regards,
>
> On Thu, Sep 13, 2018 at 8:40 AM Stefan Johansson
> <stefan.johansson at oracle.com <mailto:stefan.johansson at oracle.com>> wrote:
>
> Hi,
>
> Could you please provide the GC logs from the run as well, the reports
> give a good overview but some details from the logs might help us give
> better advise. It will also help to rule out that there are no Full GCs
> occurring as you say. Some more comments inline.
>
> On 2018-09-12 15:26, Wajih Ahmed wrote:
> > Hello,
> >
> > I have an application running on two nodes in a kubernetes
> cluster. It
> > is handling about 70 million requests per day. I have noticed a
> gradual
> > decline in the throughput so much so that in about 7 days the
> througput
> > falls about 50%. Although large percent of this decline is in
> the first
> > hour and then a gradual decline.
> > This graph
> >
> <https://drive.google.com/open?id=19pG4j2ezNj-jm69Br7HqGKtR_c7L_-r6> to
> > shows this pattern. Some of the decline i can attribute to the
> > application and use case itself. As database starts growing
> rapidly the
> > system come under memory and cpu pressure and the database itself is
> > also a java application. So perhaps ignoring the decline of the
> first
> > hour is prudent but i am still interested in seeing if i can tune
> the
> > jvm of the app so that the throughput is more linear after the
> first hour.
> >
> > I am also providing a gceasy.io <http://gceasy.io>
> <http://gceasy.io> report
> > <https://drive.google.com/open?id=1s0akdn6ztj2-oeOHwEjFMqbDRpYOweJJ>
> > that will
> > give the required information about GC activity. You will see i
> have
> > done some rudementary tuning already.
> >
> > What i am curious about is if the young gen size needs to be
> reduced by
> > tunring G1NewSizePercent to reduce the duration of the pauses in
> > particular the object copy stage.
>
> This is a very hard question and answer, a smaller young gen of course
> mean less regions to collect but since the GCs will occur more
> frequently, less objects will have time to die, so it might be that a
> larger young gen is quicker to collect for some applications. And since
> long pause times doesn't seem to be the biggest problem, I wouldn't
> start the tuning here.
>
> >
> > Secondly what GCEasy is calling "consecutive full gc" don't
> appear to be
> > full GC's. But it might be CMS (initial-mark) activity which
> accouts
> > for most of the GC activity and has some long pause times. Will
> > increasing InitiatingHeapOccupancyPercent be recommended to
> reduce this
> > activity and give the application more time?
> >
>
> Looking at the report it looks like the old generation grows over time
> and it might be that a lot of it is live so the concurrent cycles don't
> free up that much and that you still are above the limit afterwards. If
> this is the case setting a higher InitiatingHeapOccupancyPercent could
> help.
>
> Would also be helpful to know what version of Java you are running.
>
> Cheers,
> Stefan
>
> > Any other advise will be helpful as i start to learn and unfold the
> > mystries of GC tuning :-)
> >
> > Just in case you don't want to open the pdf report these are my
> JVM args
> >
> > -XX:G1MixedGCCountTarget=12 -XX:InitialHeapSize=7516192768
> > -XX:MaxGCPauseMillis=200 -XX:MaxHeapSize=7516192768 -
> > XX:MetaspaceSize=268435456 -XX:+PrintAdaptiveSizePolicy -XX:+PrintGC
> > -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
> > -XX:+PrintPromotionFailure -XX:+PrintTenuringDistribution
> > -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC
> > -XX:- UseNUMA
> >
> >
> > Regards
> >
> >
> > _______________________________________________
> > hotspot-gc-use mailing list
> > hotspot-gc-use at openjdk.java.net
> <mailto:hotspot-gc-use at openjdk.java.net>
> > http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
> >
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net <mailto:hotspot-gc-use at openjdk.java.net>
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
>
More information about the hotspot-gc-use
mailing list