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https://issues.apache.org/jira/browse/PHOENIX-852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14093072#comment-14093072
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Maryann Xue commented on PHOENIX-852:
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The approach I'm gonna take for now for join optimization is to construct an IN
clause and use it to generate skip scan filter but not as a hash set filter. In
other words, I'm gonna let the IN clause go through WhereOptimizer only, and
not through the later stages of WhereCompiler. So if the join expression
contains some key part, a skip scan will be generated to avoid a full scan
while the real join work will still be exactly the same process as it is now.
> 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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