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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17747) Support both weak and soft object pool
Date Tue, 14 Mar 2017 03:55:41 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15923510#comment-15923510
] 

Duo Zhang commented on HBASE-17747:
-----------------------------------

Oh you changed the pool type in IdReadWriteLock directly? As the jira title says 'support
both', I assume that you just introduce a new implementation and make it configurable. I'm
a little worried about the memory pressure if you use soft reference. I used to use soft reference
somewhere and got OOME...

Have you test it in the normal mode for HBase? Which GC algorithm do you use? If we want to
replace the implementation, then we need more tests before commit.

Thanks.

> Support both weak and soft object pool
> --------------------------------------
>
>                 Key: HBASE-17747
>                 URL: https://issues.apache.org/jira/browse/HBASE-17747
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 2.0
>            Reporter: Yu Li
>            Assignee: Yu Li
>             Fix For: 2.0
>
>         Attachments: HBASE-17747.patch, HBASE-17747.v2.patch, HBASE-17747.v3.patch
>
>
> During YCSB testing on embedded mode after HBASE-17744, we found that under high read
load GC is quite severe even with offheap L2 cache. After some investigation, we found it's
caused by using weak reference in {{IdReadWriteLock}}. In embedded mode the read is so quick
that the lock might already get promoted to the old generation when the weak reference is
cleared, which causes dirty card table (old reference get removed and new lock object set
into {{referenceCache}}, see {{WeakObjectPool#get}}) thus slowing YGC. In distributed mode
there'll also be more lock object created with weak reference than soft reference that slowing
down the processing.
> So we proposed to use soft reference for this {{IdReadWriteLock}} used in cache, which
won't get cleared until JVM memory is not enough, and could resolve the issue mentioned above.
What's more, we propose to extend the {{WeakObjectPool}} to be more generate to support both
weak and soft reference.
> Note that the GC issue only emerges under embedded mode with DirectOperator, in which
case all costs on the wire is removed thus produces extremely high concurrency.



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