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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-921) region close and open processed out of order; makes for disagreement between master and regionserver on region state
Date Tue, 14 Oct 2008 16:19:44 GMT

    [ https://issues.apache.org/jira/browse/HBASE-921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12639471#action_12639471
] 

stack commented on HBASE-921:
-----------------------------

Rong-en up on IRC:
{code}
[23:33]	<rafan>	btw, jim's 921 passes unit test here
{code}

> region close and open processed out of order; makes for disagreement between master and
regionserver on region state
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-921
>                 URL: https://issues.apache.org/jira/browse/HBASE-921
>             Project: Hadoop HBase
>          Issue Type: Sub-task
>    Affects Versions: 0.18.0
>            Reporter: stack
>            Assignee: Jim Kellerman
>            Priority: Blocker
>             Fix For: 0.18.1, 0.19.0
>
>         Attachments: 921-0.18.0.patch
>
>
> Master assigns region X successfully.  It then decides to close it because it wants it
opened elsewhere as part of region rebalancing.  Both the open and close operations are reported
back to the master.  Both have operation processing components that are added to the todo
list to be processed in another thread outside of the master's main loop.
> The close operation does the bulk of its work inline with the master main processing
loop.  Its todo component does some work if the region is offlined but otherwise nothing of
consequence whereas the open in its todo does the important meta catalog table update with
the new location information.
> Its been fairly common here on our cluster where the master todo queue is occupied processing
the shutdown of a regionserver.  It takes a long time to process the shutdown of a regionserver
when thousands of regions   This latter delays the processing of the open and close todos.
 In effect the open is running after the close.  The region goes into limbo.  Only a restart
of the 'hosting' regionserver 'fixes' this state.
> This is a particular case of the general HBASE-543 issue.  Its happening alot here on
our cluster so will hack up a fix for this and get it into TRUNK and backport it to 0.18.1.
> Jim Firby here had a good idea for conditions like this.  Clients should be able to say
"I've asked for a regions location 10 times now and Mr. Master, you've given me the same response
ten times in a row and each time, the answer was wrong.  Revisit any notion that said region
is at said location".  Mr. Master would then go off and do something drastic like close and
reassign the region.

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