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https://issues.apache.org/jira/browse/HBASE-1908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12766245#action_12766245
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Jonathan Gray commented on HBASE-1908:
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Patch fixes the problem. It does re-assign META, but doesn't seem to matter
(since it's being reassigned to regionserver already hosting it).
Also tested killing server hosting META instead of ROOT and all seems fine.
Did uncover a client issue though.
> ROOT not reassigned if only one regionserver left
> -------------------------------------------------
>
> Key: HBASE-1908
> URL: https://issues.apache.org/jira/browse/HBASE-1908
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.20.1
> Reporter: Jonathan Gray
> Priority: Blocker
> Fix For: 0.20.2, 0.21.0
>
> Attachments: HBASE-1908-v1.patch
>
>
> Yannis on the list uncovered an assignment bug:
> {quote}
> I performed additional testing with some alternate configurations and the
> problem arises (ONLY) when there is only one regionserver left which has the
> META table already assigned to it.
> In this case the ROOT table does not get assigned to the last regionserver
> (which holds the META table).
> Interestingly enough though when there is only one regionserver left that has
> the ROOT table already assign to it then it can also have the META table
> re-assigned to it (if again is the only server - i.e. in this scenario you
> can have one regionserver holding both the META and ROOT tables).
> Unless I am missing something I cannot find any reason why we cannot assign
> the ROOT table to the regionserver that manages the META table if it is the
> only one remaining (again it is an extreme case I agree that this can happen).
> I applied and tested a fix (at the hbase-0.20.0 codebase) in the
> RegionManager::regionsAwaitingAssignment where I add the root table in the
> regionstoAssign set if the it is the metaServer and also the only server.
> {quote}
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