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https://issues.apache.org/jira/browse/HIVE-20090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16540584#comment-16540584
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Deepak Jaiswal commented on HIVE-20090:
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cc [~jdere]
> Extend creation of semijoin reduction filters to be able to discover new
> opportunities
> --------------------------------------------------------------------------------------
>
> Key: HIVE-20090
> URL: https://issues.apache.org/jira/browse/HIVE-20090
> Project: Hive
> Issue Type: Improvement
> Components: Physical Optimizer
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Priority: Major
> Attachments: HIVE-20090.01.patch, HIVE-20090.02.patch,
> HIVE-20090.04.patch, HIVE-20090.05.patch
>
>
> Assume the following plan:
> {noformat}
> TS[0] - RS[1] - JOIN[4] - RS[5] - JOIN[8] - FS[9]
> TS[2] - RS[3] - JOIN[4]
> TS[6] - RS[7] - JOIN[8]
> {noformat}
> Currently, {{TS\[6\]}} may only be reduced with the output of {{RS\[5\]}},
> i.e., input to join between both subplans.
> However, it may be useful to consider other possibilities too, e.g., reduced
> by the output of {{RS\[1\]}} or {{RS\[3\]}}. For instance, this is important
> when, given a large plan, an edge between {{RS[5]}} and {{TS[0]}} would
> create a cycle, while an edge between {{RS[1]}} and {{TS[6]}} would not.
> This patch comprises two parts. First, it creates additional predicates when
> possible. Secondly, it removes duplicate semijoin reduction
> branches/predicates, e.g., if another semijoin that consumes the output of
> the same expression already reduces a certain table scan operator (heuristic,
> since this may not result in most efficient plan in all cases). Ultimately,
> the decision on whether to use one or another should be cost-driven
> (follow-up).
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