Seeking answer to a GC pattern

[Grzegorz Molenda]

Just a few tips:

Check OS stats for paging / swapping activity at both VM'and hypervisor
levels.

Make sure the OS doesn't use transparent huge pages.

If the above two don't help, try enabling -XX:+PrintGCTaskTimeStamps to
diagnose, which part of GC collecion takes the most time. Note values
aren't reported in time units, but in ticks. Subtract one from the other
reported per task . Compare between tasks per signle collection and check
stats from a few collections in row, to get the idea, where it does
degradate.

Thanks,

Grzegorz



2015-11-20 20:46 GMT+01:00 Jun Zhuang <jun.zhuang at hobsons.com>:

> Hi Srinivas,
>
>
>
> Thanks for your suggestion. I ran test with following parameters:
>
>
>
> -server -XX:+UseCompressedOops -XX:+TieredCompilation
> -XX:ReservedCodeCacheSize=64m -XX:+UseCodeCacheFlushing
> -XX:+PrintTenuringDistribution -Xms2g -Xmx2g -XX:MaxPermSize=256m
> -XX:NewSize=128m -XX:MaxNewSize=128m -XX:SurvivorRatio=6
> -XX:-UseAdaptiveSizePolicy -XX:+DisableExplicitGC -XX:MaxTenuringThreshold=2
>
>
>
> But the -XX:MaxTenuringThreshold=2 setting does not seem to help anything.
> I am still seeing similar GC pattern as with the +AlwaysTenure, actually
> the young GC time is higher with MTT=2 (getting to 0.5 secs vs. 0.25 with
> AlwaysTenure).
>
>
>
> Unless anyone else can provide another theory, I am convinced that
> nepotism is at play here. Changing the java startup parameters can only get
> me so far, dev will have to look at the code and see what can be done on
> the code level.
>
>
>
> Thanks,
>
> Jun
>
>
>
> *From:* Srinivas Ramakrishna [mailto:ysr1729 at gmail.com]
> *Sent:* Thursday, November 19, 2015 8:09 PM
> *To:* Jun Zhuang <jun.zhuang at hobsons.com>
> *Cc:* hotspot-gc-use at openjdk.java.net
> *Subject:* Re: Seeking answer to a GC pattern
>
>
>
> Use -XX:MaxTenuringThreshold=2 and you might see better behavior that
> +AlwaysTenure (which is almost always a very bad choice). That will at
> least reduce some of the nepotism issues from +AlwaysTenure that Thomas
> mentions. MTT > 2 is unlikely to help at your current frequency of minor
> collections since the mortality after age 1 is fairly low (from your
> tenuring distribution). Worth a quick test.
>
>
>
> -- ramki
>
>
>
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>
>
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