impala-reviews mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Marcel Kornacker (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4792: Fix number of distinct values for a CASE with constant outputs
Date Sat, 28 Jan 2017 16:28:52 GMT
Marcel Kornacker has posted comments on this change.

Change subject: IMPALA-4792: Fix number of distinct values for a CASE with constant outputs
......................................................................


Patch Set 2:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/5768/2/fe/src/main/java/org/apache/impala/analysis/CaseExpr.java
File fe/src/main/java/org/apache/impala/analysis/CaseExpr.java:

Line 384:     // Otherwise, take a max over all the outputs as well as all the slotrefs that
> Yes. The alternative is to take the max over the 'then/else exprs' and igno
hm, not sure what to do here. we could try out both variants, and i can make arguments for
both (don't throw information away; counterexample: case when a < 10 then 1 else a end
will get it really wrong if ndv(a) == -1 but in reality it has 10^9 values).

or maybe start with the -1 propagation, and then see how many benchmark queries we regress.


-- 
To view, visit http://gerrit.cloudera.org:8080/5768
To unsubscribe, visit http://gerrit.cloudera.org:8080/settings

Gerrit-MessageType: comment
Gerrit-Change-Id: I21dbdaad8452b7e58c477612b47847dccd9d98d2
Gerrit-PatchSet: 2
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Joe McDonnell <joemcdonnell@cloudera.com>
Gerrit-Reviewer: Alex Behm <alex.behm@cloudera.com>
Gerrit-Reviewer: Joe McDonnell <joemcdonnell@cloudera.com>
Gerrit-Reviewer: Marcel Kornacker <marcel@cloudera.com>
Gerrit-HasComments: Yes

Mime
View raw message