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https://issues.apache.org/jira/browse/HBASE-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268059#comment-13268059
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Zhihong Yu commented on HBASE-5494:
-----------------------------------
Introducing region-level locks requires careful consideration of various
scenarios.
e.g. consider consecutive regions R1, R2 and R3. User A wants to split R2 while
user B wants to merge the three regions, at the same time.
They both acquire table lock. Then B acquires write lock on R1 and tries to
lock R2, however A has acquired write lock on R2 at this moment. B should
release lock on R1 and retry later - otherwise R2 would not exist by the time A
completes the splitting.
> 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, D2997.4.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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