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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2700) Handle master failover for regions in transition
Date Thu, 24 Jun 2010 17:55:53 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882245#action_12882245

stack commented on HBASE-2700:

The data in zk is proxy for actual state.  It'll likely have holes, misreporting whats actually
out on the RS.  Going to the source to ask it what it actually has would seem less error-prone
(less complex), no?

Regards a second list of regionservers up in zk, could you not here also look at .META.? 
It's server cell has hostnames.  Could compare this list to whats up in zk as live RSs and
then w/ the difference, go poke around in filesystem to find logs to split?

My mine concern is that there seems to have been no consideration of how the bible addresses
this issue, if only a "we looked at it and discarded it because of 1, 2, and 3".  The zk approach
sounds like it could be 'faster' but being a representation of state, there is the possibility
that its representation may diverge from actual state.

As to keeping all in memory in master, reading the BT paper, I'm not sure if that is what
is going on.  It would seem to indicate so in the sentence where it describes how master learns
of dropped splits but as you say, for big clusters this  may prove untenable.

> Handle master failover for regions in transition
> ------------------------------------------------
>                 Key: HBASE-2700
>                 URL: https://issues.apache.org/jira/browse/HBASE-2700
>             Project: HBase
>          Issue Type: Sub-task
>          Components: master, zookeeper
>            Reporter: Jonathan Gray
>            Priority: Critical
>             Fix For: 0.21.0
> To this point in HBASE-2692 tasks we have moved everything for regions in transition
into ZK, but we have not fully handled the master failover case.  This is to deal with that
and to write tests for it.

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