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https://issues.apache.org/jira/browse/PHOENIX-852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14099422#comment-14099422
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Maryann Xue commented on PHOENIX-852:
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Since we don't have stats, it is difficult to judge whether the join key can be
narrowed to a small set of values (compared to the entire rowkey numbers). So,
again take PHOENIX-889 for example, I think it would quite make sense if we
just guess if the RHS (hash cache) will be narrowed down by looking if it's got
any filters. And if we don't do (2) for now, think we might still need to keep
those two hints.
> Optimize child/parent foreign key joins
> ---------------------------------------
>
> Key: PHOENIX-852
> URL: https://issues.apache.org/jira/browse/PHOENIX-852
> Project: Phoenix
> Issue Type: Improvement
> Reporter: James Taylor
> Assignee: Maryann Xue
>
> Often times a join will occur from a child to a parent. Our current algorithm
> would do a full scan of one side or the other. We can do much better than
> that if the HashCache contains the PK (or even part of the PK) from the table
> being joined to. In these cases, we should drive the second scan through a
> skip scan on the server side.
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