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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7403) Online Merge
Date Thu, 20 Dec 2012 13:27:12 GMT
chunhui shen created HBASE-7403:

             Summary: 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

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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