Question about RS Set size
D vd Reddy
dvdeepankar.reddy at gmail.com
Fri Feb 13 19:12:18 UTC 2015
Thanks for the reply, will try the parameters you suggested and report
On Fri, Feb 13, 2015 at 9:51 AM, Yu Zhang <yu.zhang at oracle.com> wrote:
> Hi,
>
> -XX:G1RSetRegionEntries=4096 does not control the number of regions. The
> number of regions is calculated based on G1HeapRegionSize.
> G1RSetRegionEntries decides the entries in RSet fine grain table. Since
> you set it very big, you do not see coarsening. On the other hand, this
> could increase the memory foot print a lot.
>
> The heap size is 80g, but only used maximum 60g. Reading the log you
> attached, the 1st mixed gc after marking cycle is 400ms, 2nd 458ms, 3rd
> 537ms, 4th 744ms. Since you have a lot of unused heap, you can reduce the
> mixed gcs. There are several ways to do this:
> 1. increase G1HeapWastePercent=15
> 2. decrease G1MixedGCLiveThresholdPercent=65
>
> You can try those in the order listed, or a combination.
> For you reference about those parameters please see
> https://blogs.oracle.com/g1gc/date/20140807
>
> Thanks,
> Jenny
>
> On 2/11/2015 7:54 PM, D vd Reddy wrote:
>
> 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 10 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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