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From "Hive QA (JIRA)" <>
Subject [jira] [Commented] (HIVE-8975) Possible performance regression on bucket_map_join_tez2.q
Date Mon, 08 Dec 2014 00:02:12 GMT


Hive QA commented on HIVE-8975:

{color:red}Overall{color}: -1 at least one tests failed

Here are the results of testing the latest attachment:

{color:red}ERROR:{color} -1 due to 3 failed/errored test(s), 6696 tests executed
*Failed tests:*

Test results:
Console output:
Test logs:

Executing org.apache.hive.ptest.execution.PrepPhase
Executing org.apache.hive.ptest.execution.ExecutionPhase
Executing org.apache.hive.ptest.execution.ReportingPhase
Tests exited with: TestsFailedException: 3 tests failed

This message is automatically generated.

ATTACHMENT ID: 12685635 - PreCommit-HIVE-TRUNK-Build

> Possible performance regression on bucket_map_join_tez2.q
> ---------------------------------------------------------
>                 Key: HIVE-8975
>                 URL:
>             Project: Hive
>          Issue Type: Bug
>          Components: Logical Optimizer, Statistics
>    Affects Versions: 0.15.0
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Prasanth Jayachandran
>         Attachments: HIVE-8975.1.patch, HIVE-8975.2.patch, HIVE-8975.3.patch
> After introducing the identity project removal optimization in HIVE-8435, plan in bucket_map_join_tez2.q
that runs on Tez changed to be sub-optimal. In particular, earlier it was doing a map-join
and after HIVE-8435 it changed to a reduce-join.
> The query is the following one:
> {noformat}
> select a.key, b.key from (select distinct key from tab) a join tab b on b.key = a.key
> {noformat}
> The plan before removing the projections is:
> {noformat}
> TS[0]-FIL[16]-SEL[1]-GBY[2]-RS[3]-GBY[4]-SEL[5]-RS[8]-JOIN[11]-SEL[12]-FS[13]
> TS[6]-FIL[17]-RS[10]-JOIN[11]
> {noformat}
> And after removing identity projections:
> {noformat}
> TS[0]-FIL[16]-GBY[2]-RS[3]-GBY[4]-RS[8]-JOIN[11]-SEL[12]-FS[13]
> TS[6]-FIL[17]-RS[10]-JOIN[11]
> {noformat}
> After digging a bit, I realized it is not converting the reduce-join into a map-join
because stats for GBY\[4\] change if SEL\[5\] is removed; thus the optimization does not kick
> The reason for the stats change in the GroupBy operator is in [this line|],
where it is checked whether the GBY is immediately followed by a RS operator or not, and calculate
stats differently depending on it.

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