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Date: Fri, 4 May 2012 01:14:50 +0000 (UTC)
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Subject: [jira] [Commented] (HBASE-5494) Introduce a zk hosted table-wide
 read/write lock so only one table operation at a time
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    [ https://issues.apache.org/jira/browse/HBASE-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268007#comment-13268007 ] 

Phabricator commented on HBASE-5494:
------------------------------------

avf has commented on the revision "[jira] [HBASE-5494] [89-fb] Table-level locks for schema changing operations.".

  @stack I'm currently thinking over this. I think it makes sense to have a separate JIRA (or perhaps another patch for the same JIRA?) to address this -- acquiring a table lock for merges and splits makes sense to me. Since a table lock would only serve to prevent table schema modifications (disabling/enabling schemas), it would be okay if the lock remains "stuck" during a split -- as long as there is a way to recover from this.

  I am thinking of the right way to remove persistent locks in general from a crash -- will get back to you with some thoughts on the matter.

REVISION DETAIL
  https://reviews.facebook.net/D2997

                
> Introduce a zk hosted table-wide read/write lock so only one table operation at a time
> --------------------------------------------------------------------------------------
>
>                 Key: HBASE-5494
>                 URL: https://issues.apache.org/jira/browse/HBASE-5494
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: stack
>         Attachments: D2997.3.patch
>
>
> I saw this facility over in the accumulo code base.
> Currently we just try to sort out the mess when splits come in during an online schema edit; somehow we figure we can figure all possible region transition combinations and make the right call.
> We could try and narrow the number of combinations by taking out a zk table lock when doing table operations.
> For example, on split or merge, we could take a read-only lock meaning the table can't be disabled while these are running.
> We could then take a write only lock if we want to ensure the table doesn't change while disabling or enabling process is happening.
> Shouldn't be too hard to add.

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