[jira] [Commented] (PHOENIX-1179) Support many-to-many joins

["James Taylor (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-1179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14211536#comment-14211536 ] 

James Taylor commented on PHOENIX-1179:
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Thanks for the contribution, [~maryannxue]. This is fantastic! First some high level questions before any detailed feedback:
- how is it determined if a hash-join is possible?
- is the hint USE_SORT_MERGE_JOIN an all-or-nothing hint, in that if more than two tables are joined together, they'd all use the the merge sort algorithm instead of a hash join? Should we have a way of hinting each part of the join (kind of like we have for our index order hint)?
- what's the high level algorithm? That'd be good to capture in a code comment (sorry in advance if I missed it). Does it push an ORDER BY to the server based on the join keys? What happens if there's already an ORDER BY clause?
- would be interesting to get your feedback on what we need in terms of statistics to drive the optimizer decisions: PHOENIX-1178, PHOENIX-1453, maybe others needed? [~julianhyde] may have ideas.

> Support many-to-many joins
> --------------------------
>
>                 Key: PHOENIX-1179
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1179
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Maryann Xue
>             Fix For: 3.0.0, 4.0.0, 5.0.0
>
>         Attachments: 1179.patch
>
>
> Enhance our join capabilities to support many-to-many joins where the size of both sides of the join are too big to fit into memory (and thus cannot use our hash join mechanism). One technique would be to order both sides of the join by their join key and merge sort the results on the client.



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