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From "terry zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7735) Prevent regions from moving during online snapshot.
Date Wed, 20 Mar 2013 01:55:15 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13607173#comment-13607173
] 

terry zhang commented on HBASE-7735:
------------------------------------

Hi Jonathan Hsieh´╝î  Can we use below methods to increase the probability of snapshots succeeding?

1. get all the region list in master. Including moving region , online region and spliting
region(parent and child)
2. check the region list to make sure there is no hole in it.
3. generate a snapshot task assign map file in the target snapshot folder. (also assign the
moving regions and spliting parent regions to some region server )
4. when the regionserver start buildSubprocedure. it will compare online region and the assgin
region list in task file which master generated . if it is a online region it will be a FlushSnapshotSubprocedure.
if it is not online we can think it is a close region. we do not need to flush cache , only
need to create reference file(empty file). If the region already in the snapshot folder. we
can just skip .

I think this would be helpful cause in large cluster moving region and spliting region is
a normal stituation. So snapshot maybe always fail when do the verification. what do you think
?
                
> Prevent regions from moving during online snapshot.
> ---------------------------------------------------
>
>                 Key: HBASE-7735
>                 URL: https://issues.apache.org/jira/browse/HBASE-7735
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Jonathan Hsieh
>
> To increase the probability of snapshots succeeding, we should attempt to prevent splits
and region moves from happening.  Currently we take region locks but this could be "too late"
and results in an aborted snapshot.  
> We should probably take the table lock (0.96) when starting a snapshot and for  a 0.94
backport we should probably disable the balancer.
> This will probably not be tackled until after trunk merge.

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