[Impala-ASF-CR] IMPALA-8014: Revise FK/PK cardinality estimation

["Tim Armstrong (Code Review)" <ge...@cloudera.org>]

Tim Armstrong has posted comments on this change. ( http://gerrit.cloudera.org:8080/12535 )

Change subject: IMPALA-8014: Revise FK/PK cardinality estimation
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Patch Set 5:

I've been meaning to make some time to look at this. I think my high-level concern is about potential regressions (i.e. where we were wrong for the right reasons). I know you've argued against having a flag for everything because of the configuration space, testing and code complexity problems, but I wonder if there's a way we can guard against the worst issues.

E.g. can we factor out the cardinality code into a strategy class with a simple interface to encapsulate the different versions of the logic? Can we limit the configuration space by using something coarser-grained than planner versioning, e.g. have a planner "epoch" that is incremented for a group of significant planner changes.

Definitely don't want to be stuck being overly conservative with preserving semi-broken logic, but it would be good to mitigate the risk if it can be done with reasonable effort.


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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: Id0db82564596b0a9271b89b8e3f7a3cf92d306da
Gerrit-Change-Number: 12535
Gerrit-PatchSet: 5
Gerrit-Owner: Paul Rogers <pr...@cloudera.com>
Gerrit-Reviewer: Bharath Vissapragada <bh...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <im...@cloudera.com>
Gerrit-Reviewer: Paul Rogers <pr...@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <ta...@cloudera.com>
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>
Gerrit-Comment-Date: Wed, 03 Apr 2019 00:01:21 +0000
Gerrit-HasComments: No