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From "Hari Krishna Dara (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13959) Region splitting takes too long because it uses a single thread in most common cases
Date Mon, 29 Jun 2015 08:58:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14605305#comment-14605305
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Hari Krishna Dara commented on HBASE-13959:
-------------------------------------------

Yes, I think I understand your proposal better now. Since the max storefile count should be
around the blocking store file count, it makes sense to use it as the max. However, I came
across blogs in which folks used unusually large blocking store file count (e.g., 200) to
optimize their write performance (at the cost of read performance, of course) which could
translate to having too many threads and causing resource availability and performance issues,
so perhaps we should also enforce an upper limit to the number of logical cores (as returned
by Runtime.getRuntime().availableProcessors()) ?

As a follow up change, we could also create the two references on each storefile in parallel
and shave off another 300 to 400ms in most scenarios. I can create a separate jira for this
and work on it separately once this is merged.

> Region splitting takes too long because it 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: 0.98.14
>
>         Attachments: 13959-suggest.txt, HBASE-13959-2.patch, HBASE-13959-3.patch, HBASE-13959-4.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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