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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3362) If .META. offline between OPENING and OPENED, then wrong server location in .META. is possible
Date Thu, 16 Dec 2010 08:17:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3362?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12971997#action_12971997

HBase Review Board commented on HBASE-3362:

Message from: "Jonathan Gray" <jgray@apache.org>

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Ship it!

a few small comments.  i think the loop should change as described in my comment (busy loop
w/ call to currentTimeMillis as i read it).  otherwise +1, good stuff.  we need some tickle
util class soon :)


    "on this server" should probably be left in comment to be clear what this is checking


    We were not previously but we should probably log this condition


    This is a busy wait loop?
    Should we add a wait/notify on something passed to the thread and w/ a timeout of the
    And then we should probably also have some kind of max timeout.  Even if minutes, there
could be weird cluster state where the RS misses META availability but someone else might
handle it properly, so max timeout might be good?




    maybe this should be warn.  i think i'd want to see it and also logging of stack trace
(i don't see logging of it elsewhere)

- Jonathan

> If .META. offline between OPENING and OPENED, then wrong server location in .META. is
> ----------------------------------------------------------------------------------------------
>                 Key: HBASE-3362
>                 URL: https://issues.apache.org/jira/browse/HBASE-3362
>             Project: HBase
>          Issue Type: Bug
>            Reporter: stack
>            Assignee: stack
>            Priority: Critical
>             Fix For: 0.90.0
> This is a good one.  It happened to me testing OOME in split logging.
> * Balancer moves region to new location, regionservrer X.
> * New location regionserver X successfully opens the region and then goes to update .META.
> * At this point, the server carrying .META. crashes.
> * Regionserver X is stuck waiting on .META. to come back online.  It takes so long master
times out the region-in-transition
> * Master assigns the region elsewhere to regionserver Y
> * It opens successfully on regionserver Y and then it also parks waiting on .META. coming
> * .META. comes online
> * The two servers X and Y race to update .META.
> I saw case where server X edit went in after server Ys edit which means that lookups
in .META. get the wrong server.  HBCK can detect this situation.
> RegionServer X when it wakes up coreeclty notices that its lost control of the region
but the damage is done -- where damage is .META. edit.
> Chatting with Jon, he suggested that regionserver X should 'rollback' the .META. edit
-- do explicit delete of what it added.  This would work I think but chatting more, I'll make
a fix that keeps updating the zookeeper OPENING state while edit goes on in a separate thread.
 Our continuous setting of OPENING will make it so region-in-transition does not timeout.

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