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https://issues.apache.org/jira/browse/HIVE-22238?focusedWorklogId=439078&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-439078
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ASF GitHub Bot logged work on HIVE-22238:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 30/May/20 14:08
Start Date: 30/May/20 14:08
Worklog Time Spent: 10m
Work Description: kgyrtkirk closed pull request #831:
URL: https://github.com/apache/hive/pull/831
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Issue Time Tracking
-------------------
Worklog Id: (was: 439078)
Time Spent: 50m (was: 40m)
> 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
> Fix For: 4.0.0
>
> 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, HIVE-22238.06.patch, HIVE-22238.06.patch,
> HIVE-22238.07.patch, HIVE-22238.09.patch, HIVE-22238.10.patch,
> HIVE-22238.10.patch, HIVE-22238.10.patch, HIVE-22238.10.patch
>
> Time Spent: 50m
> 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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