Need help on G1 GC young gen Update RS and Scan RS pause reduction

[charlie hunt]

> “- from one gc to another, just for these four gcs, sys time is relatively high.”

Assuming this is on Linux … perhaps double check that THP (transparent huge pages) is disabled.

charlie

> On Feb 3, 2017, at 7:01 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi Amit,
> 
> On Fri, 2017-02-03 at 11:09 +0000, Amit Mishra wrote:
>> Hi Thomas/team,
>> 
>> 
>> I have put all parameters as per your suggestion but somehow the
>> minor gc pauses are still haunting.
>> 
>> Attaching GC logs.
>> 
>> 
>> bash-3.2$ grep -i young gcstats.log.10636|cut -d, -f2|awk -F" "
>> '{print $1}'|awk '$1 > 1'
>> 1.1273134
>> 1.1683221
>> 3.5504848
>> 5.2693987
> 
>   looking at these log entries, there seems to be something going on
> that seems outside of VM control:
> 
> - from one gc to another, just for these four gcs, sys time is
> relatively high.
> 
> - for the last two occurrences, at least one thread is hanging in "Ext
> Root Scanning" for almost all of the gc time for no obvious reason.
> 
> - there do not seem to be an unusually large amount of changes in the
> amount of work done in the particular phases that would raise immediate
> concerns to me.
> 
> Please try to find out the source of the high sys time and maybe even
> what causes it. I can't help a lot in that area, but dtrace seems a
> good starting point as suggested earlier.
> 
> I think we went through most obvious tunings now, but maybe somebody else has more ideas. I don't at this time.
> 
> The jdk (7u45) you are using is also very old, so even if we find that
> there is something wrong with g1 in particular, I kind of doubt there
> are many more useful knobs to turn with that version (or even
> appropriate logging to find out about the actual issue). Since 7u45
> release, there have been hundreds of changes that in particular improve
> G1 performance, so please consider upgrading to something more recent
> (at least latest 8u, preferably to me some test runs with 9ea).
> Upgrading alone might already help.
> 
> Thanks,
>   Thomas
> 
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