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From "Ashutosh Chauhan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-20491) Fix mapjoin size estimations for Fast implementation
Date Tue, 04 Sep 2018 16:08:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-20491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16603246#comment-16603246
] 

Ashutosh Chauhan commented on HIVE-20491:
-----------------------------------------

[~kgyrtkirk] Selection of kind of hashtable is done by Vectorizer which runs *after* ConvertJoinMapJoin
which does algo selection. I see you have updated size computation assuming fast hashtable
but wont it better that we first do memory computation using optimized version and then using
fast. If fast qualifies set that in Join so that vectorizer can pick correct hashtable type?
Though, since fast hashtables are bigger current approach also works though its more conservative
than needed.

> Fix mapjoin size estimations for Fast implementation
> ----------------------------------------------------
>
>                 Key: HIVE-20491
>                 URL: https://issues.apache.org/jira/browse/HIVE-20491
>             Project: Hive
>          Issue Type: Improvement
>          Components: Statistics
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>            Priority: Major
>         Attachments: HIVE-20491.01.patch, HIVE-20491.01wip02.patch, HIVE-20491.02.patch
>
>
> HIVE-19824 have fixed the estimations; but it calculated for the "optimized" impl; the
"fast" one has a little bit bigger footprint.
> It also seems like fast is a bit overestimated at runtime...that should be also taken
care of.
> | numkeys | implementation | compiler estimation | runtime estimation | runtime measurement
| ce / rm | re / rm |
> | 25M | FAST | 1168435456 | 2189433712 | 1513584984 | .77 | 1.44 |
> | 25M | OPTIMIZED | 1168435456 | 1191203764 | 1168439664 | 100% | 1.01 |



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