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From "Hari Krishna Dara (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13959) Region splitting uses a single thread in most common cases
Date Tue, 30 Jun 2015 12:15:06 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14608198#comment-14608198
] 

Hari Krishna Dara commented on HBASE-13959:
-------------------------------------------

bq. Let's create a new one.

I will create a "Brainstorming" issue to start a discussion on this and capture requirements.

bq. Be very careful, though, for correctness it is essential that the daughter come online
in the correct order (daughter B first). Or at least are made visible in META in that order.

This is actually a very local operation and so should be safe (bringing the daughters online
comes outside this scope). I just created HBASE-13999 for this.


> Region splitting uses a single thread in most common cases
> ----------------------------------------------------------
>
>                 Key: HBASE-13959
>                 URL: https://issues.apache.org/jira/browse/HBASE-13959
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.98.12
>            Reporter: Hari Krishna Dara
>            Assignee: Hari Krishna Dara
>            Priority: Critical
>             Fix For: 2.0.0, 0.98.14, 1.0.2, 1.2.0, 1.1.2, 1.3.0
>
>         Attachments: 13959-0.98.txt, 13959-suggest.txt, HBASE-13959-2.patch, HBASE-13959-3.patch,
HBASE-13959-4.patch, HBASE-13959-5.patch, HBASE-13959.patch, region-split-durations-compared.png
>
>
> When storefiles need to be split as part of a region split, the current logic uses a
threadpool with the size set to the size of the number of stores. Since most common table
setup involves only a single column family, this translates to having a single store and so
the threadpool is run with a single thread. However, in a write heavy workload, there could
be several tens of storefiles in a store at the time of splitting, and with a threadpool size
of one, these files end up getting split sequentially.
> With a bit of tracing, I noticed that it takes on an average of 350ms to create a single
reference file, and splitting each storefile involves creating two of these, so with a storefile
count of 20, it takes about 14s just to get through this phase alone (2 reference files for
each storefile), pushing the total time the region is offline to 18s or more. For environments
that are setup to fail fast, this makes the client exhaust all retries and fail with NotServingRegionException.
> The fix should increase the concurrency of this operation.



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