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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7247) Assignment performances decreased by 50% because of regionserver.OpenRegionHandler#tickleOpening
Date Fri, 30 Nov 2012 18:45:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13507536#comment-13507536
] 

stack commented on HBASE-7247:
------------------------------

Moving znode from OPENING to OPENING or CLOSING to CLOSING ensuring the sequence numbers are
as we expect is how we check we still have 'ownership' of the region before we go about making
alterations in the filesystem.  The callback the master gets when we 'update' the znode is
used to flag the master that the region server is still 'alive' and working on the opening
so the master updates its opening timer when it gets the callback.

It is imperfect in that we could lose the lease between the check and the fs operation.

Alternatives would be to remove this mechanism and instead just rely on our getting a callback
if the znode is taken from us?  This would happen in another thread.  Would have to be watching.
 This would seem to coarser than what we currently have widening the window during which we
could do fs operations on a region though we've lost ownership.  Master would not get notification
that a region server is opening a region only its taking longer than usual.

Any other suggestions?
                
> Assignment performances decreased by 50% because of regionserver.OpenRegionHandler#tickleOpening
> ------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-7247
>                 URL: https://issues.apache.org/jira/browse/HBASE-7247
>             Project: HBase
>          Issue Type: Improvement
>          Components: master, Region Assignment, regionserver
>    Affects Versions: 0.96.0
>            Reporter: nkeywal
>            Assignee: nkeywal
>            Priority: Critical
>
> The regionserver.OpenRegionHandler#tickleOpening updates the region znode as "Do this
so master doesn't timeout this region-in-transition.".
> However, on the usual test, this makes the assignment time of 1500 regions goes from
70s to 100s, that is, we're 50% slower because of this.
> More generally, ZooKeper commits to disk all the data update, and this takes time. Using
it to provide a keep alive seems overkill. At the very list, it could be made asynchronous.
> I'm not sure how necessary these updates are required (I need to go deeper in the internal,
feedback welcome), but it seems very important to optimize this... The trival fix would be
to make this optional.

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