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https://issues.apache.org/jira/browse/TAJO-1352?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14624401#comment-14624401
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ASF GitHub Bot commented on TAJO-1352:
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Github user hyunsik commented on the pull request:
https://github.com/apache/tajo/pull/593#issuecomment-120859618
Not all changes are shown in the diff in github due to lots of changes. So,
I leave some comments here.
* ```cachekey``` in ```JoinGraphContext``` should be changed to a local
member variable. Its cache effect is trivial because the object lifecycle is
very short.
* the member variable LOG in GreedyHeuristicJoinOrderAlgorithm is added
but is not used.
* PlannerUtil::isSymmetricJoin includes the comment about commutative.
But, the method name has been changed from isCommutativeJoin to
isSymmetricJoin. As far as I know, commutative join is used in common for the
exact meaning we know. But, symmetric join is not usual. Please see two links:
symmetric join (https://goo.gl/d4uOO3) vs. commutative join
(https://goo.gl/oFCgtM).
I'm still reviewing the patch. I'll give more comments soon.
> Improve the join order algorithm to consider missed cases of associative join
> operators
> ---------------------------------------------------------------------------------------
>
> Key: TAJO-1352
> URL: https://issues.apache.org/jira/browse/TAJO-1352
> Project: Tajo
> Issue Type: Improvement
> Components: planner/optimizer
> Reporter: Jihoon Son
> Assignee: Jihoon Son
> Attachments: JoinGraph.png
>
>
> TAJO-1277 fixes a bug related to the associativity of join operators, but
> there are still some missed cases that join operators are associative. This
> work should include the cases described in the following links:
> * http://stackoverflow.com/questions/20022196/are-left-outer-joins-associative
> * https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Joins
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