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https://issues.apache.org/jira/browse/ASTERIXDB-1086?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15427229#comment-15427229
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Taewoo Kim commented on ASTERIXDB-1086:
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This is part of index-only change and is uploaded as a patch set:
https://asterix-gerrit.ics.uci.edu/#/c/1073/
> IntroduceProjectsRule creates a wrong PROJECT operator when there are
> multiple paths.
> -------------------------------------------------------------------------------------
>
> Key: ASTERIXDB-1086
> URL: https://issues.apache.org/jira/browse/ASTERIXDB-1086
> Project: Apache AsterixDB
> Issue Type: Bug
> Components: AsterixDB, Optimizer
> Reporter: Taewoo Kim
> Assignee: Taewoo Kim
> Labels: with-index-only
>
> IntroduceProjectsRule introduce a wrong project to filter out a variable that
> is used in the one of two paths after SPLIT (REPLICATE) operator. In my
> branch, I am trying to optimize the index-search. In order to implement this,
> there is an ASSIGN operator and it assigns a variable that is going to be
> used in the SELECT operator. After ASSIGN, there is SPLIT operator. It
> divides the path into two - the left path contains the SELECT and the other
> path contains no operator. Two paths will be merged by UNION operator. The
> issue is IntroduceProjectRule can't consider all paths at the same time.
> Thus, when it checks the right path, it introduces a wrong PROJECT operator
> that filters out one variable in the ASSIGN before SPLIT since it thinks that
> the variable is not used after ASSIGN operator. In fact, the variable is used
> in the left path.
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