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https://issues.apache.org/jira/browse/HIVE-12492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15877214#comment-15877214
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Ashutosh Chauhan commented on HIVE-12492:
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I am not sure if patch is working as intended. For 2-way join, A DHJ is
selected with 2 CUSTOM_SIMPLE_EDGE going into Reducer where join operator is of
type MapJoin.
None of the test cases in attached patch has plans of that shape.
See: ql/src/test/results/clientpositive/llap/tez_dynpart_hashjoin_*.q.out
> 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
> Attachments: 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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