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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7721) Local Transactions in META
Date Sat, 02 Feb 2013 03:10:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569405#comment-13569405
] 

Enis Soztutar commented on HBASE-7721:
--------------------------------------

bq. Could punt on this a while given .META. does not split currently (We should allow it split
one day to spread the load and to make it so less damage done if only a piece of .META. is
offline because of server crash rather than all).
Agreed. It means we do not actually need a split policy for now. In HBASE-7748, I added a
delimited key prefix split policy, which can be deployed in META table. 
Do you remember why we have disabled META splits in the first place? 
bq. Why you say this Enis?
Just to list our options. If we move to ZK in META, we don't need this issue. However, that
discussion is out of scope for this issue I guess. 
                
> Local Transactions in META
> --------------------------
>
>                 Key: HBASE-7721
>                 URL: https://issues.apache.org/jira/browse/HBASE-7721
>             Project: HBase
>          Issue Type: Improvement
>          Components: Coprocessors, regionserver
>            Reporter: Enis Soztutar
>            Assignee: Enis Soztutar
>             Fix For: 0.96.0
>
>
> Thanks to Lars' local transactions patch (HBASE-5229), we can entertain the possibility
of doing local transactions within META regions.
> We need this mainly for region splits and merges. Clients scan the META concurrent to
the split/merge operations, and to prevent the clients from seeing overlapping region boundaries
or holes in META, we just through hoops. For more backgroun, see BlockingMetaScannerVisitor,
HBASE-5986, and my comments at https://reviews.apache.org/r/8716/. 
> Now, for the actual implementation options: 
>  1. As outlined in http://hadoop-hbase.blogspot.com/2012_02_01_archive.html, 
>    - We have to implement a Custom RegionSplitPolicy for the META regions to ensure that
a table's regions are always co-located in the same META region. Then we can add MultiRowMutationEndpoint
as a system level coprocessor, and use it for META operations. 
>  2. Do smt like HBASE-7716, and expose local atomic multi-row operations as a native
API.
>  3. Move META to zookeeper. Use zookeeper.multi.  
> Then we can change region split / merge logic to make use of atomic META operations.

> Thoughts, suggestions? 

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