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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17434) New Synchronization Scheme for Compaction Pipeline
Date Mon, 09 Jan 2017 12:37:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15811674#comment-15811674

Eshcar Hillel commented on HBASE-17434:

This is the same as in DefaultMemstote - the active segment is moved to snapshot and only
then removed from active.
A get operation that is executed concurrent with a flush to disk can have a scanner on active
and a scanner on the same segment in snapshot. The duplication is eliminated in the final
result, and same goes for CompactingMemStore.

> 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, HBASE-17434-V03.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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