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From "ASF GitHub Bot (Jira)" <j...@apache.org>
Subject [jira] [Work logged] (HIVE-22238) PK/FK selectivity estimation underscales estimations
Date Fri, 01 Nov 2019 05:34:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-22238?focusedWorklogId=337194&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-337194
]

ASF GitHub Bot logged work on HIVE-22238:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 01/Nov/19 05:33
            Start Date: 01/Nov/19 05:33
    Worklog Time Spent: 10m 
      Work Description: jcamachor commented on pull request #831: HIVE-22238 pkfk
URL: https://github.com/apache/hive/pull/831#discussion_r341452795
 
 

 ##########
 File path: ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java
 ##########
 @@ -2255,8 +2259,14 @@ private long getCardinality(List<Operator<? extends OperatorDesc>>
ops, Integer
         Statistics parentStats = parent.getStatistics();
         if (fkInd == pos) {
           // 2.1 This is the new number of rows after PK is joining with FK
-          newrows = (long) Math.ceil(parentStats.getNumRows() * pkfkSelectivity);
+          if (isFkFiltered) {
+            // if the foregin key is filtered by some condition we may not rescale it
 
 Review comment:
   typo: `foregin`
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 337194)
    Time Spent: 0.5h  (was: 20m)

> PK/FK selectivity estimation underscales estimations
> ----------------------------------------------------
>
>                 Key: HIVE-22238
>                 URL: https://issues.apache.org/jira/browse/HIVE-22238
>             Project: Hive
>          Issue Type: Bug
>          Components: Statistics
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HIVE-22238.01.patch, HIVE-22238.02.patch, HIVE-22238.03.patch, HIVE-22238.04.patch,
HIVE-22238.05.patch, HIVE-22238.05.patch, HIVE-22238.05.patch, HIVE-22238.05.patch, HIVE-22238.05.patch
>
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> at [this point|https://github.com/apache/hive/blob/5098d155a1e6a164253f5fa98755273bc34085df/ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java#L2182]
the parent operators rownum is scaled according to pkfkselectivity
> however [pkfkselectivity is computed|https://github.com/apache/hive/blob/5098d155a1e6a164253f5fa98755273bc34085df/ql/src/java/org/apache/hadoop/hive/ql/optimizer/stats/annotation/StatsRulesProcFactory.java#L2157]
on a whole subtree.
> Scaling it by that amount will count in estimation already used when parentstats was
calculated...so depending on the number of upstream joins - this may lead to severe underestimations
> what happened was:
> * optimization was able to push the filter to the other side of the join
> * as a result the incoming data was already filtered
> * scaling down by the PK selectiviy - was actually already there...but a new "scaling"
happened



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