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https://issues.apache.org/jira/browse/PHOENIX-1556?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16369777#comment-16369777
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Maryann Xue commented on PHOENIX-1556:
--------------------------------------

Thank you, [~rajeshbabu], for reminding me! 5.x branch has now caught up with 
all my recent check-ins.

> Base hash versus sort merge join decision on cost
> -------------------------------------------------
>
>                 Key: PHOENIX-1556
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1556
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Maryann Xue
>            Priority: Major
>              Labels: CostBasedOptimization
>             Fix For: 4.14.0
>
>         Attachments: PHOENIX-1556.patch
>
>
> At compile time, we know how many guideposts (i.e. how many bytes) will be 
> scanned for the RHS table. We should, by default, base the decision of using 
> the hash-join verus many-to-many join on this information.
> Another criteria (as we've seen in PHOENIX-4508) is whether or not the tables 
> being joined are already ordered by the join key. In that case, it's better 
> to always use the sort merge join.



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