Multi-second ParNew collections but stable CMS

[Jon Masamitsu]

Ashwin,

You sent a sample GC log with a fast ParNew (about 31ms) right?  Can you 
send
examples of the slow ParNew's?  I'd like to see what I can see in the logs
that is changing from the fast GC's to the slower GC's.  If I can 
download a complete
log, that would be useful (there is a size limit on what you can mail to 
the list so
mailing might not work).

Jon


On 12/16/2014 8:47 PM, Ashwin Jayaprakash wrote:
> Hi, we have a cluster of ElasticSearch servers running with 31G heap 
> and OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode).
>
> While our old gen seems to be very stable with about 40% usage and no 
> Full GCs so far, our young gen keeps growing from ~50MB to 850MB every 
> few seconds. These ParNew collections are taking anywhere between 1-7 
> seconds and is causing some of our requests to time out. The eden 
> space keeps filling up and then cleared every 30-60 seconds. There is 
> definitely work being done by our JVM in terms of caching/buffering 
> objects for a few seconds, writing to disk and then clearing the 
> objects (typical Lucene/ElasticSearch indexing and querying workload)
>
> These long pauses are not good for our server throughput and I was 
> doing some reading. I got some conflicting reports on how Cassandra is 
> configured compared to Hadoop. There are also references 
> <http://blog.mgm-tp.com/2013/12/benchmarking-g1-and-other-java-7-garbage-collectors/> 
> to this old ParNew+CMS bug 
> <http://bugs.java.com/view_bug.do?bug_id=6459113> which I thought 
> would've been addressed in the JRE version we are using. Cassandra 
> recommends 
> <http://aryanet.com/blog/cassandra-garbage-collector-tuning> a larger 
> NewSize with just 1 for max tenuring, whereas Hadoop recommends 
> <http://wiki.apache.org/hadoop/PerformanceTuning> a small NewSize.
>
> Since most of our allocations seem to be quite short lived, is there a 
> way to avoid these "long" young gen pauses?
>
> Thanks in advance. Here are some details.
> *
> Heap settings:*
> java -Xmx31000m -Xms31000m
> -Xss512k -XX:MaxPermSize=512m -XX:ReservedCodeCacheSize=64m
> -XX:+UseConcMarkSweepGC -XX:+UseCMSInitiatingOccupancyOnly 
> -XX:CMSInitiatingOccupancyFraction=70
> -XX:+UseParNewGC -XX:+ScavengeBeforeFullGC -XX:+PrintPromotionFailure
> -XX:+PrintClassHistogramBeforeFullGC -XX:+PrintTenuringDistribution
> -XX:GCLogFileSize=512m -XX:NumberOfGCLogFiles=2 -XX:+PrintGCDateStamps
> -XX:+UseGCLogFileRotation -XX:+DisableExplicitGC 
> -XX:PrintFLSStatistics=1 -XX:+PrintGCDetails
>
> *
> Last few lines of "kill -3 pid" output:*
> Heap
>  par new generation   total 996800K, used 865818K [0x00007fa18e800000, 
> 0x00007fa1d2190000, 0x00007fa1d2190000)
>   eden space 886080K,  94% used [0x00007fa18e800000, 
> 0x00007fa1c1a659e0, 0x00007fa1c4950000)
>   from space 110720K,  25% used [0x00007fa1cb570000, 
> 0x00007fa1cd091078, 0x00007fa1d2190000)
>   to   space 110720K,   0% used [0x00007fa1c4950000, 
> 0x00007fa1c4950000, 0x00007fa1cb570000)
>  concurrent mark-sweep generation total 30636480K, used 12036523K 
> [0x00007fa1d2190000, 0x00007fa920000000, 0x00007fa920000000)
>  concurrent-mark-sweep perm gen total 128856K, used 77779K 
> [0x00007fa920000000, 0x00007fa927dd6000, 0x00007fa940000000)
> *
> *
> *Sample gc log:*
> 2014-12-11T23:32:16.121+0000: 710.618: [ParNew
> Desired survivor size 56688640 bytes, new threshold 6 (max 6)
> - age   1:    2956312 bytes,    2956312 total
> - age   2:     591800 bytes,    3548112 total
> - age   3:      66216 bytes,    3614328 total
> - age   4:     270752 bytes,    3885080 total
> - age   5:     615472 bytes,    4500552 total
> - age   6:     358440 bytes,    4858992 total
> : 900635K->8173K(996800K), 0.0317340 secs] 
> 1352217K->463460K(31633280K)After GC:
> Statistics for BinaryTreeDictionary:
> ------------------------------------
> Total Free Space: -433641480
> Max   Chunk Size: -433641480
> Number of Blocks: 1
> Av.  Block  Size: -433641480
> Tree      Height: 1
> After GC:
> Statistics for BinaryTreeDictionary:
> ------------------------------------
> Total Free Space: 1227
> Max   Chunk Size: 631
> Number of Blocks: 3
> Av.  Block  Size: 409
> Tree      Height: 3
> , 0.0318920 secs] [Times: user=0.38 sys=0.01, real=0.03 secs]
>
>
> Ashwin Jayaprakash.
>
>
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