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From "Juan Yu (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-5483: Automatically disable codegen for small queries
Date Wed, 21 Jun 2017 21:29:29 GMT
Juan Yu has posted comments on this change.

Change subject: IMPALA-5483: Automatically disable codegen for small queries
......................................................................


Patch Set 3:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/7153/3//COMMIT_MSG
Commit Message:

PS3, Line 15: a plan node
> MaxRowsProcessedVisitor detects when there are missing or corrupt stats and
Multi-column PK is not uncommon. Even with accurate stats, Planner could generate wrong plan,
accidentally put small table on left side, and underestimate the join cardinality.
I maybe too conservative. My philosophy is codegen is good in general, we should disable it
only when we are certain it will be slow. when we are not certain, keep it as before. That
can reduce the risk of regression. Maybe do the same as the small query optimization, skip
join for now until we can do better estimations.
Also some logging or indication in plan the codegen is disabled due to this optimization will
help troubleshooting.


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Gerrit-MessageType: comment
Gerrit-Change-Id: I273bcee58641f5b97de52c0b2caab043c914b32e
Gerrit-PatchSet: 3
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-Reviewer: Juan Yu <jyu@cloudera.com>
Gerrit-Reviewer: Michael Ho
Gerrit-Reviewer: Michael Ho <kwho@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-HasComments: Yes

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