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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17434) New Synchronization Scheme for Compaction Pipeline
Date Sun, 08 Jan 2017 21:06:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15810016#comment-15810016
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Eshcar Hillel commented on HBASE-17434:
---------------------------------------

I also prefer read-write lock over an exclusive lock when there is a potential performance
boost. However I don't think this is the case.
Flush and in-memory compaction which invoke getVersionedList/Tail later invoke swap. These
operations are only once in a while, so it is not the case where we have multiple concurrent
(read-only) operations contending on the lock and a read lock can reduce the contention.
On the flip side using ReentrantReadWriteLock adds an additional lock instead of using existing
locks as in the synchronize mechanism (and the code is more complicated with the try-final
blocks).


> New Synchronization Scheme for Compaction Pipeline
> --------------------------------------------------
>
>                 Key: HBASE-17434
>                 URL: https://issues.apache.org/jira/browse/HBASE-17434
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Eshcar Hillel
>            Assignee: Eshcar Hillel
>         Attachments: HBASE-17434-V01.patch, HBASE-17434-V02.patch
>
>
> A new copyOnWrite synchronization scheme is introduced for the compaction pipeline.
> The new scheme is better since it removes the lock from getSegments() which is invoked
in every get and scan operation, and it reduces the number of LinkedList objects that are
created at runtime, thus can reduce GC (not by much, but still...).
> In addition, it fixes the method getTailSize() in compaction pipeline. This method creates
a MemstoreSize object which comprises the data size and the overhead size of the segment and
needs to be atomic.



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