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From "Henry Robinson (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4456: Change query exec state lock to a reader-writer lock
Date Thu, 10 Nov 2016 23:17:47 GMT
Henry Robinson has posted comments on this change.

Change subject: IMPALA-4456: Change query_exec_state_lock_ to a reader-writer lock
......................................................................


Patch Set 3:

Once concern I have is about fairness. It's pretty critical that writers don't get starved
out of this lock because that prevents queries from starting or finishing. 

If there's enough demand for the reader-side of the lock such that there's really no period
at which the lock is free for writers, I can see a starvation situation happening. 

This doesn't happen right now because all once the lock is released, there is always a period
(however small) where the lock is available for taking. You might need to think about an external
mechanism to prevent new readers from taking the lock when a writer is waiting. That would
make things more complicated, so let me know if you have any better ideas.

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Gerrit-MessageType: comment
Gerrit-Change-Id: I790a95e7179f07aa7ba188d5422c5e054353ba0b
Gerrit-PatchSet: 3
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Sailesh Mukil <sailesh@cloudera.com>
Gerrit-Reviewer: Henry Robinson <henry@cloudera.com>
Gerrit-Reviewer: Sailesh Mukil <sailesh@cloudera.com>
Gerrit-HasComments: No

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