Question about RS Set size

Thu Feb 12 04:00:14 UTC 2015

Hi,
    Thanks for the reply.If the region size is capped then GC will not be
adhering to the regionCount mentioned right?

Also yes the high scanRS is in mixed GC, Can you suggest the tunings /
experiments so that we can reduce this.
The parameters we run with are (we also ran with MaxGCPause to 200 we saw
similar things)

*-XX:MaxGCPauseMillis=100 -XX:G1HeapRegionSize=32m
-XX:InitiatingHeapOccupancyPercent=65 -XX:G1ReservePercent=20
-XX:G1HeapWastePercent=5 -XX:G1MixedGCLiveThresholdPercent=75
-XX:G1RSetRegionEntries=4096*

I am attaching a part of the log that covers the run for around 6 min
(Bigger log for a day here
https://raw.githubusercontent.com/dvdreddy/gc-logs/master/g1-gc.log) .  I
am also pasting in the mail a sample mixed GC run here for quick review,
you can see that ScanRS and Object copy are at the same level
2015-02-09T10:10:25.491-0500: 5383952.213: [GC pause (mixed)
Desired survivor size 285212672 bytes, new threshold 3 (max 15)
- age   1:   65081144 bytes,   65081144 total
- age   2:  136289896 bytes,  201371040 total
- age   3:  122469928 bytes,  323840968 total
 5383952.213: [G1Ergonomics (CSet Construction) start choosing CSet,
_pending_cards: 23323, predicted base time: 42.39 ms, remaining time: 57.61
ms, target pause time:\
 100.00 ms]
 5383952.213: [G1Ergonomics (CSet Construction) add young regions to CSet,
eden: 114 regions, survivors: 17 regions, predicted young region time:
28.59 ms]
 5383952.214: [G1Ergonomics (CSet Construction) finish adding old regions
to CSet, reason: predicted time is too high, predicted time: 1.30 ms,
remaining time: 0.00 ms\
, old: 107 regions, min: 107 regions]
 5383952.214: [G1Ergonomics (CSet Construction) added expensive regions to
CSet, reason: old CSet region num not reached min, old: 107 regions,
expensive: 60 regions, \
min: 107 regions, remaining time: 0.00 ms]
 5383952.214: [G1Ergonomics (CSet Construction) finish choosing CSet, eden:
114 regions, survivors: 17 regions, old: 107 regions, predicted pause time:
170.47 ms, targ\
et pause time: 100.00 ms]
 5383952.388: [G1Ergonomics (Mixed GCs) continue mixed GCs, reason:
candidate old regions available, candidate old regions: 743 regions,
reclaimable: 12156413304 bytes\
 (13.82 %), threshold: 5.00 %]
, 0.1751220 secs]
   [Parallel Time: 131.1 ms, GC Workers: 23]
      [GC Worker Start (ms): Min: 5383952214.8, Avg: 5383952215.2, Max:
5383952215.5, Diff: 0.7]
      [Ext Root Scanning (ms): Min: 5.4, Avg: 6.1, Max: 9.6, Diff: 4.3,
Sum: 140.5]
      [Update RS (ms): Min: 3.7, Avg: 6.7, Max: 7.7, Diff: 4.0, Sum: 154.8]
         [Processed Buffers: Min: 9, Avg: 14.6, Max: 22, Diff: 13, Sum: 335]
      [Scan RS (ms): Min: 50.9, Avg: 51.2, Max: 51.4, Diff: 0.5, Sum:
1178.2]
      [Object Copy (ms): Min: 65.3, Avg: 65.6, Max: 66.1, Diff: 0.8, Sum:
1507.9]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.5]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum:
1.5]
      [GC Worker Total (ms): Min: 129.4, Avg: 129.7, Max: 130.2, Diff: 0.8,
Sum: 2983.3]
      [GC Worker End (ms): Min: 5383952344.9, Avg: 5383952344.9, Max:
5383952345.1, Diff: 0.2]
   [Code Root Fixup: 0.0 ms]
   [Clear CT: 7.8 ms]
   [Other: 36.2 ms]
      [Choose CSet: 1.6 ms]
      [Ref Proc: 6.1 ms]
      [Ref Enq: 0.1 ms]
      [Free CSet: 3.8 ms]
   [Eden: 3648.0M(3648.0M)->0.0B(3808.0M) Survivors: 544.0M->384.0M Heap:
56.6G(81.9G)->50.6G(81.9G)]
 [Times: user=3.10 sys=0.00, real=0.18 secs]

On Wed, Feb 11, 2015 at 5:31 PM, Yu Zhang <yu.zhang at oracle.com> wrote:

>  Hi,
>
> Currently the region size is capped at 32MB.
>
> It is good that you confirmed there is no coarsening. Is the high scanRS
> in mixed gc?  If it is, then there are some tunings you can try to reduce
> it.
>
> Thanks,
> Jenny
>
> On 2/11/2015 4:12 PM, D vd Reddy wrote:
>
>
> Hi,
>       we are using G1 GC for heap size of about 92 - 96 GB and we observed
> in the logs that Scan RS times were too high (comparable to Object Copy
> time, Is this normal ?, I have checked that there are no coarsening(s)). So
> in order to counter that we plan to decrease the region count, currently we
> set it explicitly to 4096 with regionSize to 32MB. My question is that if
> we drop setting regionSize and decrease the regions to 2048 what will
> happen to region size, Can it go above 32 MB and keep the regions to 2048
> or is it capped at 32MB ?
>
>
>  Thanks in advance
>
>
>
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>
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