G1gc compaction algorithm

Thu Aug 7 00:14:31 UTC 2014

Hi!

Thanks. We were currently running 4M with wastepercent=0 but unfortunately
don't have any logs for that.

Will try "-XX:G1HeapRegionSize=16m -XX:G1HeapWastePercent=10
-XX:G1RSetRegionEntries=1792 -XX:G1RSetSparseRegionEntries=40" and post
results later back here.

**
Martin

2014-08-07 0:53 GMT+03:00 Yu Zhang <yu.zhang at oracle.com>:

>  Martin,
>
> Thanks for the logs and following up with us.
>
> In this chart, the purple line is the ScanRS time for mixed gc.  At the
> bottom there are grey circles indicating when the initial mark happens.
> The white is the ScanRS time for mixed gc with to-space exhausted.
>
>
> You can see that the first several scanRS after initial-mark is ok, then
> they go up to 7000ms.  For the 16m region size runs, you have
> G1HeapWastePercent=0. (4m region size has G1HeapWastePercent=1).  Because
> of this, g1 will not stop mixed gc till there is no candidate regions.
> From the space claimed by mixed gc, it claims 2-3g heap, but the price is
> too high.  Another disadvantage is it does not start marking phases:
> "do not request concurrent cycle initiation, reason: still doing mixed
> collections, occupancy: 2147483648 bytes, allocation request: 0 bytes,
> threshold: 2147483640 bytes (10.00 %), source: end of GC]"
>
> If you look at the claimable heap in MB, 4m heap region size starts mixed
> gc at lower reclaimable
>
>
> Another thing is there are coarsening for RSet Entries.
>
> Can you do one with
> -XX:G1HeapRegionSize=16m -XX:G1HeapWastePercent=10
> -XX:G1RSetRegionEntries=1792 -XX:G1RSetSparseRegionEntries=40
>
> Thanks,
> Jenny
>
> On 8/4/2014 9:33 AM, Martin Makundi wrote:
>
> Hi!
>
> Here are the fresh logs:
>
>  http://81.22.250.165/log/gc-16m-2014-08-04.log
>
>  Today we were hit by quite some number of Full GC's with quite short
> intervals and as can be suspected, not so happy users ;)
>
>  Any ideas? I will reduce the region size to 4M for now, because it
> resulted in much fewer full gcs.
>
>  **
> Martin
>
>
>  2014-08-01 1:17 GMT+03:00 Martin Makundi <
> martin.makundi at koodaripalvelut.com>:
>
>> Hmm.. ok, I copy pasted if from the mail, it works after typing manually,
>> thanks.
>>
>>  Problem seems to have been BOTH a whitespace typo AND
>> UnlockDiagnosticOptions was on the right side.
>>
>>  Thanks.
>>
>>  Gathering logs now.
>>
>>  **
>> Martin
>>
>>
>> 2014-08-01 1:01 GMT+03:00 Yu Zhang <yu.zhang at oracle.com>:
>>
>>  maybe some hidden text?
>>>
>>> Thanks,
>>> Jenny
>>>
>>>  On 7/31/2014 2:52 PM, Martin Makundi wrote:
>>>
>>> Strange that it is in the property summary but doesn't allow setting it.
>>>
>>>
>>> 2014-08-01 0:39 GMT+03:00 Martin Makundi <
>>> martin.makundi at koodaripalvelut.com>:
>>>
>>>> Hi!
>>>>
>>>> UnlockDiagnosticVMOptions  is on (though later (on the right side) in
>>>> the command line). Jvm version is
>>>>
>>>>  java version "1.7.0_55"
>>>> Java(TM) SE Runtime Environment (build 1.7.0_55-b13)
>>>> Java HotSpot(TM) 64-Bit Server VM (build 24.55-b03, mixed mode)
>>>>
>>>>
>>>>
>>>> 2014-08-01 0:37 GMT+03:00 Yu Zhang <yu.zhang at oracle.com>:
>>>>
>>>>  Martin,
>>>>>
>>>>> These 2 need to run with  -XX:+UnlockDiagnosticVMOptions
>>>>>
>>>>> Thanks,
>>>>> Jenny
>>>>>
>>>>>  On 7/31/2014 2:33 PM, Martin Makundi wrote:
>>>>>
>>>>> Hi!
>>>>>
>>>>>  G1SummarizeRSetStats does not seem to work, jvm says:
>>>>>
>>>>>  Improperly specified VM option 'G1SummarizeRSetStatsPeriod=10'
>>>>> Error: Could not create the Java Virtual Machine.
>>>>> Error: A fatal exception has occurred. Program will exit.
>>>>>
>>>>>  Same for both new options
>>>>>
>>>>>
>>>>>
>>>>> 2014-07-31 20:22 GMT+03:00 Yu Zhang <yu.zhang at oracle.com>:
>>>>>
>>>>>> Martin,
>>>>>>
>>>>>> The ScanRS for mixed gc is extremely long, 1000-9000ms.  Because it
>>>>>> is over pause time goal, minimum old regions can be added to CSet.  So
>>>>>> mixed gc is not keeping up.
>>>>>>
>>>>>> Can do a run keeping 16m region size,  no G1PrintRegionLivenessInfo,
>>>>>> no PrintHeapAtGC.  But -XX:+G1SummarizeRSetStats
>>>>>> -XX:G1SummarizeRSetStatsPeriod=10
>>>>>>
>>>>>> This should tell us more about RSet information.
>>>>>>
>>>>>> While the UpdateRS is not as bad as ScanRS, we can try to push it to
>>>>>> the concurrent threads.  Can you add -XX:G1RSetUpdatingPauseTimePercent=5.
>>>>>>  I am hoping this brings the UpdateRS down to 50ms.
>>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Jenny
>>>>>>
>>>>>> On 7/28/2014 8:27 PM, Martin Makundi wrote:
>>>>>>
>>>>>>> Hi!
>>>>>>>
>>>>>>> We suffered a couple of Full GC's using regionsize 5M (it seems to
>>>>>>> be exact looking at logged actual parameters) and we tried the 16M option
>>>>>>> and this resulted in more severe Full GC behavior.
>>>>>>>
>>>>>>> Here is the promised log for 16 M setting:
>>>>>>> http://81.22.250.165/log/gc-16m.log
>>>>>>>
>>>>>>> We switch back to 5M hoping it will behave more nicely.
>>>>>>>
>>>>>>> **
>>>>>>> Martin
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>
>
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