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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11126) Add RegionObserver pre hooks that operate under row lock
Date Wed, 28 May 2014 05:06:01 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14010781#comment-14010781
] 

ramkrishna.s.vasudevan commented on HBASE-11126:
------------------------------------------------

bq.In case of replay the KV's TS wont be latestTS. So actually it wont get called.
Ya.  That was a case when we don't update the delete cells with LONG.MIN_VALUE in case we
don't find matching KVs with visibility expression.
I thought better to handle it in this patch also so that we are sure that the CP hooks are
not called.  Adding before prepareDeleteTimestamps() is also fine with me.

> Add RegionObserver pre hooks that operate under row lock
> --------------------------------------------------------
>
>                 Key: HBASE-11126
>                 URL: https://issues.apache.org/jira/browse/HBASE-11126
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.99.0, 0.98.3
>            Reporter: Andrew Purtell
>            Assignee: ramkrishna.s.vasudevan
>         Attachments: HBASE-11126.patch, HBASE-11126_1.patch, HBASE-11126_new_2.patch,
HBASE-11126_new_3.patch
>
>
> The coprocessor hooks were placed outside of row locks. This was meant to sidestep performance
issues arising from significant work done within hook invocations. However as the security
code increases in sophistication we are now running into concurrency issues trying to use
them as a result of that early decision. Since the initial introduction of coprocessor upcalls
there has been some significant refactoring done around them and concurrency control in core
has become more complex. This is potentially an issue for many coprocessor users.
> We should do either:\\
> - Move all existing RegionObserver pre* hooks to execute under row lock.
> - Introduce a new set of RegionObserver pre* hooks that execute under row lock, named
to indicate such.
> The second option is less likely to lead to surprises.
> All RegionObserver hook Javadoc should be updated with advice to the coprocessor implementor
not to take their own row locks in the hook. If the current thread happens to already have
a row lock and they try to take a lock on another row, there is a deadlock risk.
> As always a drawback of adding hooks is the potential for performance impact. We should
benchmark the impact and decide if the second option above is a viable choice or if the first
option is required.
> Finally, we should introduce a higher level interface for managing the registration of
'user' code for execution from the low level hooks. I filed HBASE-11125 to discuss this further.



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