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From "Jonathan Hsieh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7290) Online snapshots
Date Tue, 11 Dec 2012 17:39:22 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7290?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529155#comment-13529155

Jonathan Hsieh commented on HBASE-7290:

It is not a concurrency problem at that granularity. 

The situation is a coarse-grained problem.  The key problem is that writes that shouldn't
be replayed (since they don't belong to the restored image), would not normally get replayed,
but would potentially get replayed if recovery was triggered.

Previously, without restore, we could depend on the timestamps -- if something was replayed
but there was newer data, the newer data would win.  In a restore situation, the "newer" data
is has the old time stamps from before recovery, and new data that shouldn't get replayed
could be.

1) write 100 rows
2) ss1 (with logs)
3) write 50 rows
4) restore ss1
5) crash
6) writes from 1 and 3 both get replayed in log splitting recovery.   Oops.
> Online snapshots 
> -----------------
>                 Key: HBASE-7290
>                 URL: https://issues.apache.org/jira/browse/HBASE-7290
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Jonathan Hsieh
> HBASE-6055 will be closed when the offline snapshots pieces get merged with trunk.  This
umbrella issue has all the online snapshot specific patches.  This will get merged once one
of the implementations makes it into trunk.  Other flavors of online snapshots can then be
done as normal patches instead of on a development branch.

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