regarding long young generation pause when using G1 GC

[charlie hunt]

Hi Amit,

To add to Jenny’s comments …

In the absence of looking at the entire GC log and looking only at the entry included in email, this line really catches my eye:
[Times: user=184.95 sys=34.49, real=148.07 secs] 

- This is pretty high sys time. If this is Linux, check that transparent huge pages are disabled. If that’s disabled, then you may be paging to virtual memory. In short, need to chase down the root of that high sys time.
- Comparing user=184.95 to real=148.07 you do not much parallelism, ~ 1.24x. That is not much parallelism for a multi-threaded young GC.

hths,

charlie

> On Jan 21, 2016, at 12:12 PM, Yu Zhang <yu.zhang at oracle.com> wrote:
> 
> Amit,
> 
> Which jdk version are you using?
> 
> You give MaxGCPauseMillis=500, but it seems g1 is adjusting eden size too big, up to 13g. I am curious why. Can you add a flag -XX:+PrintAdaptiveSizePolicy? Meanwhile, to reduce young gc pause, can you try to a smaller number for MaxGCPauseMillis, or give a smaller eden size?
> 
> Another thing I noticed, whenever you have long gc pause, the system cpu is high. Maybe the system is busy doing something else?
> Thanks,
> Jenny
> On 1/21/2016 4:30 AM, Amit Mishra wrote:
>> Hello team,
>>  
>> Please help me with G1 GC long young generation pause..
>>  
>> At one of our Customer deployment we were using CMS with 48G heap size and facing Concurrent mode failure every month.
>>  
>> To solve this we started load test using G1 GC on lab but we are seeing intermittent long GC pause as long as 148 seconds,
>>  
>> Could you please look into logs and confirm what best we can do to ascertain root cause and possible tuning to fix this.
>>  
>> Thanks for help in advance.
>> We are using default GC parameters:(Attaching full GC file as well)
>>  
>> JVM_ARGS="${JVM_ARGS} -XX:-OmitStackTraceInFastThrow"
>> JVM_ARGS="${JVM_ARGS} -XX:-UseSSE42Intrinsics"
>> JVM_ARGS="${JVM_ARGS} -XX:-ReduceInitialCardMarks"
>> JVM_ARGS="${JVM_ARGS} -XX:+UseG1GC"
>> JVM_ARGS="${JVM_ARGS} -XX:MaxGCPauseMillis=500" 
>> JVM_ARGS="${JVM_ARGS} -XX:+UseCompressedOops" 
>> JVM_ARGS="${JVM_ARGS} -XX:+PrintFlagsFinal" 
>> JVM_ARGS="${JVM_ARGS} -XX:-EliminateLocks"
>> JVM_ARGS="${JVM_ARGS} -XX:+UseLargePages"
>> export GC_LOG="${PROJECT_HOME}/log/gcstats.log.$$"
>> JVM_ARGS=$JVM_ARGS" -Xloggc:${GC_LOG}"
>> JVM_ARGS=$JVM_ARGS" -verbose:gc"
>> JVM_ARGS="${JVM_ARGS} -XX:+DisableExplicitGC"
>> JVM_ARGS=$JVM_ARGS" -XX:+AggressiveOpts"
>> JVM_ARGS="${JVM_ARGS} -XX:+HeapDumpOnOutOfMemoryError"
>> JVM_ARGS="${JVM_ARGS} -XX:ReservedCodeCacheSize=128m"
>> JVM_ARGS="${JVM_ARGS} -XX:PermSize=256m"
>> JVM_ARGS="${JVM_ARGS} -XX:MaxPermSize=256m"
>> JVM_ARGS="${JVM_ARGS} -Xmx28672m"
>> JVM_ARGS="${JVM_ARGS} -Xms28672m
>>  
>> Long GC pause.
>>  
>> 5020.853: [GC pause (young), 148.0343389 secs]
>>    [Parallel Time: 142474.3 ms, GC Workers: 13]
>>       [GC Worker Start (ms): Min: 5022695.7, Avg: 5022705.6, Max: 5022714.4, Diff: 18.7]
>>       [Ext Root Scanning (ms): Min: 143.0, Avg: 2550.5, Max: 6442.5, Diff: 6299.4, Sum: 33157.1]
>>       [Update RS (ms): Min: 5704.6, Avg: 19017.1, Max: 45977.9, Diff: 40273.3, Sum: 247222.7]
>>          [Processed Buffers: Min: 0, Avg: 26.9, Max: 291, Diff: 291, Sum: 350]
>>       [Scan RS (ms): Min: 70538.2, Avg: 92539.7, Max: 114688.0, Diff: 44149.8, Sum: 1203016.2]
>>       [Object Copy (ms): Min: 894.7, Avg: 9265.9, Max: 20674.1, Diff: 19779.4, Sum: 120456.9]
>>       [Termination (ms): Min: 10169.3, Avg: 19073.0, Max: 26684.1, Diff: 16514.7, Sum: 247949.3]
>>       [GC Worker Other (ms): Min: 0.1, Avg: 4.5, Max: 18.2, Diff: 18.0, Sum: 58.4]
>>       [GC Worker Total (ms): Min: 142441.2, Avg: 142450.8, Max: 142461.1, Diff: 19.8, Sum: 1851860.7]
>>       [GC Worker End (ms): Min: 5165155.6, Avg: 5165156.4, Max: 5165162.0, Diff: 6.4]
>>    [Code Root Fixup: 2.2 ms]
>>    [Clear CT: 11.2 ms]
>>    [Other: 5546.7 ms]
>>       [Choose CSet: 0.0 ms]
>>       [Ref Proc: 47.4 ms]
>>       [Ref Enq: 0.9 ms]
>>       [Free CSet: 3642.1 ms]
>>    [Eden: 13.2G(13.2G)->0.0B(1416.0M) Survivors: 16.0M->16.0M Heap: 24.7G(28.0G)->11.5G(28.0G)]
>>  [Times: user=184.95 sys=34.49, real=148.07 secs] 
>>  
>> 
>> Thanks,
>> Amit
>> 
>> 
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