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Date: Wed, 6 Mar 2013 19:26:16 +0000 (UTC)
From: "Lars Hofhansl (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12624812.1356009924397.393496.1362597976386@arcas>
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Subject: [jira] [Commented] (HBASE-7403) Online Merge
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    [ https://issues.apache.org/jira/browse/HBASE-7403?page=3Dcom.atlassian=
.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1359=
5007#comment-13595007 ]=20

Lars Hofhansl commented on HBASE-7403:
--------------------------------------

Let's prove this out in trunk first. Then we can make separate decisions ab=
out other release.
0.90 and 0.92 are out of the question (imho), so might 0.94 (as this needs =
a lot of other plumbing - table locks, atomic META updates, etc)
               =20
> Online Merge
> ------------
>
>                 Key: HBASE-7403
>                 URL: https://issues.apache.org/jira/browse/HBASE-7403
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.95.0, 0.94.6
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>            Priority: Critical
>             Fix For: 0.95.0
>
>         Attachments: 7403-trunkv5.patch, 7403-trunkv6.patch, 7403v5.diff,=
 7403-v5.txt, 7403v5.txt, hbase-7403-94v1.patch, hbase-7403-trunkv10.patch,=
 hbase-7403-trunkv11.patch, hbase-7403-trunkv12.patch, hbase-7403-trunkv13.=
patch, hbase-7403-trunkv14.patch, hbase-7403-trunkv15.patch, hbase-7403-tru=
nkv16.patch, hbase-7403-trunkv1.patch, hbase-7403-trunkv5.patch, hbase-7403=
-trunkv6.patch, hbase-7403-trunkv7.patch, hbase-7403-trunkv8.patch, hbase-7=
403-trunkv9.patch, merge region.pdf
>
>
> The feature of this online merge:
> 1.Online,no necessary to disable table
> 2.Less change for current code, could applied in trunk,0.94 or 0.92,0.90
> 3.Easy to call merege request, no need to input a long region name, only =
encoded name enough
> 4.No limit when operation, you don't need to tabke care the events like S=
erver Dead, Balance, Split, Disabing/Enabing table, no need to take care wh=
ether you send a wrong merge request, it has alread done for you
> 5.Only little offline time for two merging regions
> Usage:
> 1.Tool: =20
> bin/hbase org.apache.hadoop.hbase.util.OnlineMerge [-force] [-async] [-sh=
ow] <table-name> <region-encodedname-1> <region-encodedname-2>
> 2.API: static void MergeManager#createMergeRequest
> We need merge in the following cases=EF=BC=9A
> 1.Region hole or region overlap, can=E2=80=99t be fix by hbck
> 2.Region become empty because of TTL and not reasonable Rowkey design
> 3.Region is always empty or very small because of presplit when create ta=
ble
> 4.Too many empty or small regions would reduce the system performance(e.g=
. mslab)
> Current merge tools only support offline and are not able to redo if exce=
ption is thrown in the process of merging, causing a dirty data
> For online system, we need a online merge.
> This implement logic of this patch for  Online Merge is :
> For example, merge regionA and regionB into regionC
> 1.Offline the two regions A and B
> 2.Merge the two regions in the HDFS(Create regionC=E2=80=99s directory, m=
ove regionA=E2=80=99s and regionB=E2=80=99s file to regionC=E2=80=99s direc=
tory, delete regionA=E2=80=99s and regionB=E2=80=99s directory)
> 3.Add the merged regionC to .META.
> 4.Assign the merged regionC
> As design of this patch , once we do the merge work in the HDFS,we could =
redo it until successful if it throws exception or abort or server restart,=
 but couldn=E2=80=99t be rolled back.=20
> It depends on
> Use zookeeper to record the transaction journal state, make redo easier
> Use zookeeper to send/receive merge request
> Merge transaction is executed on the master
> Support calling merge request through API or shell tool
> About the merge process, please see the attachment and patch

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