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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7403) Online Merge
Date Mon, 07 Jan 2013 17:30:15 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7403?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13546068#comment-13546068

ramkrishna.s.vasudevan commented on HBASE-7403:

bq.We receive the merge request in a zookeeper event handler, and I don't want to check the
above situation in that handler because that handler is synchronized

Ok makes sense.

bq.It is a new merge request, but we can't get the regioninfo of merging regions, it seems
user send a wrong request.

But i felt like, while doing complete_merging if due to some reason we dont get regioninfo
and we retry why not the same thing happen here in CREATE_MERGE too.

bq.see SSH#processDeadRegion and RegionMergeManager#mergingRegions
Thanks.  I missed it in the code.

bq.I think the Merger thread should read the znode and try to restart the merge right?

Don't think am asking this again. My point was does the failed merge transaction, restart
again on master restart?
Because the resubmit queue is going to be empty right?  Should we forcefully read the merge
znode and completed the failed merge as do for SPLIT.

Thanks for your answers.
> Online Merge
> ------------
>                 Key: HBASE-7403
>                 URL: https://issues.apache.org/jira/browse/HBASE-7403
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.94.3
>            Reporter: chunhui shen
>            Assignee: chunhui shen
>             Fix For: 0.96.0, 0.94.5
>         Attachments: 7403-trunkv5.patch, 7403-trunkv6.patch, 7403v5.diff, 7403-v5.txt,
7403v5.txt, hbase-7403-94v1.patch, hbase-7403-trunkv1.patch, hbase-7403-trunkv5.patch, hbase-7403-trunkv6.patch,
hbase-7403-trunkv7.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
> 4.No limit when operation, you don't need to tabke care the events like Server Dead,
Balance, Split, Disabing/Enabing table, no need to take care whether you send a wrong merge
request, it has alread done for you
> 5.Only little offline time for two merging regions
> We need merge in the following cases:
> 1.Region hole or region overlap, can’t 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 table
> 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 exception 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’s directory, move regionA’s and
regionB’s file to regionC’s directory, delete regionA’s and regionB’s 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’t be rolled back.

> 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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