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https://issues.apache.org/jira/browse/HIVE-20983?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mustafa Iman updated HIVE-20983:
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Status: Patch Available (was: Open)
> Vectorization: Scale up small hashtables, when collisions are detected
> ----------------------------------------------------------------------
>
> Key: HIVE-20983
> URL: https://issues.apache.org/jira/browse/HIVE-20983
> Project: Hive
> Issue Type: Bug
> Reporter: Gopal V
> Assignee: Mustafa Iman
> Priority: Major
> Attachments: HIVE-20983.1.patch, HIVE-20983.2.patch
>
>
> Hive's hashtable estimates are getting better with HyperLogLog stats in
> place, but an accurate estimate does not always result in a low number of
> collisions.
> The hashtables which contain a very small number of items tend to lose their
> O(1) lookup performance where there are collisions. Since collisions are easy
> to detect within the fast hashtable implementation, a rehashing to a higher
> size will help these small hashtables avoid collisions and go back to O(1)
> perf.
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