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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7245) Recovery on failed snapshot restore
Date Mon, 03 Dec 2012 20:31:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13509013#comment-13509013

Ted Yu commented on HBASE-7245:

The discussion from HBASE-6721 is related in this regard.
Francis started with storing group information on hdfs. Later he switched to storage in table.
Whether storing in zookeeper is under review.

I am fine with storing operation directive on hdfs.
> Recovery on failed snapshot restore
> -----------------------------------
>                 Key: HBASE-7245
>                 URL: https://issues.apache.org/jira/browse/HBASE-7245
>             Project: HBase
>          Issue Type: Sub-task
>          Components: Client, master, regionserver, snapshots, Zookeeper
>            Reporter: Jonathan Hsieh
>            Assignee: Matteo Bertozzi
>             Fix For: hbase-6055, 0.96.0
> Restore will do updates to the file system and to meta.  it seems that an inopportune
failure before meta is completely updated could result in an inconsistent state that would
require hbck to fix.
> We should define what the semantics are for recovering from this.  Some suggestions:
> 1) Fail Forward (see some log saying restore's meta edits not completed, then gather
information necessary to build it all from fs, and complete meta edits.).
> 2) Fail backwards (see some log saying restore's meta edits not completed, delete incomplete
snapshot region entries from meta.)  
> I think I prefer 1 -- if two processes end somehow updating  (somehow the original master
didn't die, and a new one started up) they would be idempotent.  If we used 2, we could still
have a race and still be in a bad place.

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