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Posted to issues@hive.apache.org by "Lefty Leverenz (JIRA)" <ji...@apache.org> on 2017/09/21 03:23:00 UTC

[jira] [Commented] (HIVE-17308) Improvement in join cardinality estimation

    [ https://issues.apache.org/jira/browse/HIVE-17308?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16174202#comment-16174202 ] 

Lefty Leverenz commented on HIVE-17308:
---------------------------------------

Doc note:  This changes the default value of *hive.stats.correlated.multi.key.joins* to true.

No TODOC3.0 label is needed because it will be documented for HIVE-16298, which created *hive.stats.correlated.multi.key.joins* in the same release (3.0.0).

> Improvement in join cardinality estimation
> ------------------------------------------
>
>                 Key: HIVE-17308
>                 URL: https://issues.apache.org/jira/browse/HIVE-17308
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Planning
>            Reporter: Vineet Garg
>            Assignee: Vineet Garg
>         Attachments: HIVE-17308.1.patch, HIVE-17308.2.patch, HIVE-17308.3.patch, HIVE-17308.4.patch, HIVE-17308.5.patch, HIVE-17308.6.patch, HIVE-17308.7.patch, HIVE-17308.8.patch
>
>
> Currently during logical planning join cardinality is estimated assuming no correlation among join keys (This estimation is done using exponential backoff). Physical planning on the other hand consider correlation for multi keys and uses different estimation. We should consider correlation during logical planning as well.



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