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https://issues.apache.org/jira/browse/HIVE-20491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16598822#comment-16598822
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Zoltan Haindrich commented on HIVE-20491:
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I've looked into this a little bit more...and there seems to be 2 core fast
implementations and 1 optimized.
There is a Fast implementation for long keys; and another which for
string/other keys; in case of these complex keys the optimized implementation
handles memory better.
> 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
>
> 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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