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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8163) MemstoreChunkPool: An improvement for JAVA GC when using MSLAB
Date Thu, 21 Mar 2013 02:19:15 GMT
chunhui shen created HBASE-8163:
-----------------------------------

             Summary: 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


*Background*:
When we use mslab,we will copy the keyvalue together in a structure called *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%+*


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