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From "Lefty Leverenz (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-14018) Make IN clause row selectivity estimation customizable
Date Sat, 18 Jun 2016 04:40:05 GMT

    [ https://issues.apache.org/jira/browse/HIVE-14018?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15337522#comment-15337522
] 

Lefty Leverenz commented on HIVE-14018:
---------------------------------------

Doc note:  This adds *hive.stats.filter.in.factor* to HiveConf.java, so it will need to be
documented for releases 2.1.1 and 2.2.0.

* [Configuration Properties -- Statistics | https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-Statistics]

Added TODOC2.1.1 and TODOC2.2 labels.

> Make IN clause row selectivity estimation customizable
> ------------------------------------------------------
>
>                 Key: HIVE-14018
>                 URL: https://issues.apache.org/jira/browse/HIVE-14018
>             Project: Hive
>          Issue Type: Improvement
>          Components: Statistics
>    Affects Versions: 2.1.0, 2.2.0
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Jesus Camacho Rodriguez
>            Priority: Minor
>              Labels: TODOC2.1.1, TODOC2.2
>             Fix For: 2.2.0, 2.1.1
>
>         Attachments: HIVE-14018.1.patch, HIVE-14018.patch
>
>
> After HIVE-13287 went in, we calculate IN clause estimates natively (instead of just
dividing incoming number of rows by 2). However, as the distribution of values of the columns
is considered uniform, we might end up heavily underestimating/overestimating the resulting
number of rows.
> This issue is to add a factor that multiplies the IN clause estimation so we can alleviate
this problem. The solution is not very elegant, but it is the best we can do until we have
histograms to improve our estimate.



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