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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8163) MemStoreChunkPool: An improvement for JAVA GC when using MSLAB
Date Thu, 21 Mar 2013 19:09:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13609321#comment-13609321
] 

stack commented on HBASE-8163:
------------------------------

[~zjushch] Can we guarantee that pool size is 0 when memstores are full or near full?

[~lhofhansl] "If it is too big you'll waste space, if it is too small you'll just offset the
GC for a bit."

Agree that pool should not be above and beyond memstore allocation.  Regards your comment
that we just offset GC for a bit, don't we offset it period if successful reuse?
                
> MemStoreChunkPool: An improvement for JAVA GC when using MSLAB
> --------------------------------------------------------------
>
>                 Key: HBASE-8163
>                 URL: https://issues.apache.org/jira/browse/HBASE-8163
>             Project: HBase
>          Issue Type: New Feature
>          Components: regionserver
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>         Attachments: hbase-8163v1.patch, hbase-8163v2.patch
>
>
> *Background*:
> When we use mslab,we will copy the keyvalue together in a structure called *MemStoreLAB$Chunk*,
therefore we could decrease the heap fragment. 
> *Problem*:
> When one chunk is full, we will create a new chunk, and then the old chunk will be reclaimed
by JVM if no reference to it.
> Mostly the chunk object would be promoted when doing Young GC, cause increasing the cost
of YGC 
> When a Chunk object has no reference? It should meet two following condition:
> 1.Memstore which this chunk belongs to is flushed
> 2.No scanner is opening on the memstore which this chunk belongs to
> *Solution:*
> 1.Create a chunk pool to manage the no-reference chunks, instead of being reclaimed by
JVM
> 2.When a Chunk has no reference, put it back to the pool
> 3.The pool has a max capacity, it will skip the chunks when achieve the max size
> 4.When we need new Chunk to store KeyValue, get it from the pool if exists, else create
new one by pool, so we could be able to reuse the old chunks
> *Test results:*
> Environment:
> hbase-version:0.94
> -Xms4G -Xmx4G -Xmn2G
> Row size=50 bytes, Value size=1024 bytes
> 50 concurrent theads per client, insert 10,000,000 rows
> Before:
> Avg write request per second:12953
> After testing, final result of jstat -gcutil :
> YGC YGCT FGC FGCT GCT 
> 747 36.503 48 2.492 38.995
> After:
> Avg write request per second:14025
> After testing, final result of jstat -gcutil :
> YGC YGCT FGC FGCT GCT 
> 711 20.344 4 0.284 20.628
> *Improvement: YGC 40+%; WPS 5%+*
> review board :
> https://reviews.apache.org/r/10056/

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