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From "Taras Bobrovytsky (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4939, IMPALA-4939: Decimal V2 multiplication
Date Thu, 07 Sep 2017 23:42:18 GMT
Taras Bobrovytsky has posted comments on this change.

Change subject: IMPALA-4939, IMPALA-4939: Decimal V2 multiplication
......................................................................


Patch Set 4:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/7438/4//COMMIT_MSG
Commit Message:

Line 75: DECIMAL_V2 disabled: 2.65s
> So we go down this path for multiplies that overflow, or are close to overf
Running perf top showed that most of the time is spent in ScaleDownAndRound<int256_t, int256_t>().
It looks like it's the division (of one int256 by another int256) that is taking the most
time.

I also noticed that disabling the codegen slows down the query in the BEFORE case by ~10x.
So the performance difference before my patch and after is huge only when codegen is enabled.
Otherwise, it's like a 3x difference. (Do you think it's most likely due to the scanner being
much faster in the codegen case?)


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Gerrit-MessageType: comment
Gerrit-Change-Id: I37ad6232d7953bd75c18dc86e665b2b501a1ebe1
Gerrit-PatchSet: 4
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Michael Ho <kwho@cloudera.com>
Gerrit-Reviewer: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-Reviewer: Zach Amsden <zamsden@cloudera.com>
Gerrit-HasComments: Yes

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