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From "Hiroshi Ikeda (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14708) Use copy on write Map for region location cache
Date Thu, 05 Nov 2015 03:15:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14991038#comment-14991038
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Hiroshi Ikeda commented on HBASE-14708:
---------------------------------------

It is quite confusing that some of methods provide copies, and some of methods expose the
internal data that the client should not modify. If you decide to copy all, you might have
to copy not only submaps but also entry sets, key sets, value collections, and entries (TreeMap's
entry is not thread safe).

> Use copy on write Map for region location cache
> -----------------------------------------------
>
>                 Key: HBASE-14708
>                 URL: https://issues.apache.org/jira/browse/HBASE-14708
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client
>    Affects Versions: 1.1.2
>            Reporter: Elliott Clark
>            Assignee: Elliott Clark
>            Priority: Critical
>             Fix For: 2.0.0, 1.2.0, 1.3.0
>
>         Attachments: HBASE-14708-v10.patch, HBASE-14708-v11.patch, HBASE-14708-v12.patch,
HBASE-14708-v2.patch, HBASE-14708-v3.patch, HBASE-14708-v4.patch, HBASE-14708-v5.patch, HBASE-14708-v6.patch,
HBASE-14708-v7.patch, HBASE-14708-v8.patch, HBASE-14708-v9.patch, HBASE-14708.patch, anotherbench.zip,
location_cache_times.pdf, result.csv
>
>
> Internally a co-worker profiled their application that was talking to HBase. > 60%
of the time was spent in locating a region. This was while the cluster was stable and no regions
were moving.
> To figure out if there was a faster way to cache region location I wrote up a benchmark
here: https://github.com/elliottneilclark/benchmark-hbase-cache
> This tries to simulate a heavy load on the location cache. 
> * 24 different threads.
> * 2 Deleting location data
> * 2 Adding location data
> * Using floor to get the result.
> To repeat my work just run ./run.sh and it should produce a result.csv
> Results:
> ConcurrentSkiplistMap is a good middle ground. It's got equal speed for reading and writing.
> However most operations will not need to remove or add a region location. There will
be potentially several orders of magnitude more reads for cached locations than there will
be on clearing the cache.
> So I propose a copy on write tree map.



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