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https://issues.apache.org/jira/browse/HBASE-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13267905#comment-13267905
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Phabricator commented on HBASE-5494:
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avf has commented on the revision "[jira] [HBASE-5494] [89-fb] Table-level
locks for schema changing operations.".
@stack Thanks for the comments! If we convert ZNode contents for this to
protobufs, we should also add a commands to the HBase shell (I'll be willing to
help with that) to list currently held locks (who they are held by, for what
purpose, and by whom) and delete them -- the reason they're in plain text in
the current code is to allow operations to use the ZK CLI to do so.
I agree that using protobufs would be more appropriate for this purpose, as
long as there's a way for operators to view this data without having to write
code.
INLINE COMMENTS
src/main/java/org/apache/hadoop/hbase/master/HMaster.java:1315 Right now
locking is not exposed in the client APIs, so essentially if locks are disabled
schema changes (the only part where locks are currently used) behave as they
would prior to the patch.
Should I, perhaps, add a warning in this case? ("warning: schema modification
locks are disabled, concurrent schema changes may result in corruption")
src/main/java/org/apache/hadoop/hbase/master/TableLockManager.java:67 No, in
this case I enforce (with an IllegalStateException) that locks can only be
released by their owners. Currently, stale locks (locks after a "hard" server
crash) would be removed using the ZooKeeper CLI.
It would probably make sense to add a command to the HBase shell to list all
locks currently held (and when they acquired), and then release them.
src/main/java/org/apache/hadoop/hbase/master/TableLockManager.java:111
Thanks, will do.
src/main/java/org/apache/hadoop/hbase/master/TableLockManager.java:137 I am
using an IllegalStateException to enforce this as an invariant (if a lock was
acquired in ZooKeeper, it should not be in acquiredTableLock -- and vice versa).
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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