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https://issues.apache.org/jira/browse/HIVE-12492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15887496#comment-15887496
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Lefty Leverenz commented on HIVE-12492:
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Doc note: This adds *hive.auto.convert.join.hashtable.max.entries* to
HiveConf.java, so it needs to be documented in the wiki.
* [Configuration Properties -- Query and DDL Execution |
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-QueryandDDLExecution]
Added a TODOC2.2 label.
Typo alert: In the parameter description, "does not take affect" should be
"does not take effect." This can be corrected in the wiki.
> MapJoin: 4 million unique integers seems to be a probe plateau
> --------------------------------------------------------------
>
> Key: HIVE-12492
> URL: https://issues.apache.org/jira/browse/HIVE-12492
> Project: Hive
> Issue Type: Improvement
> Components: Query Planning
> Affects Versions: 1.3.0, 1.2.1, 2.0.0
> Reporter: Gopal V
> Assignee: Jesus Camacho Rodriguez
> Labels: TODOC2.2
> Fix For: 2.2.0
>
> Attachments: HIVE-12492.01.patch, HIVE-12492.02.patch,
> HIVE-12492.patch
>
>
> After 4 million keys, the map-join implementation seems to suffer from a
> performance degradation.
> The hashtable build & probe time makes this very inefficient, even if the
> data is very compact (i.e 2 ints).
> Falling back onto the shuffle join or bucket map-join is useful after 2^22
> items.
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