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Posted to issues@calcite.apache.org by "Chunwei Lei (JIRA)" <ji...@apache.org> on 2019/08/07 06:30:00 UTC

[jira] [Commented] (CALCITE-482) Implement sql and planner hints

    [ https://issues.apache.org/jira/browse/CALCITE-482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16901774#comment-16901774 ] 

Chunwei Lei commented on CALCITE-482:
-------------------------------------

Thank you for pushing this forward, [~danny0405].  I have implemented a hint called {{selectivity}}  for the filter a long time ago like the way you propose. The difficult problem we meet is that how to deal with it after a rule fires. Should we keep the hint? Or should we merge the hint? Besides, we have to change everywhere the filter is created which is a big change. I think you have to deal with these problems too. It would be great it if you can provide a design doc.

> Implement sql and planner hints
> -------------------------------
>
>                 Key: CALCITE-482
>                 URL: https://issues.apache.org/jira/browse/CALCITE-482
>             Project: Calcite
>          Issue Type: Bug
>    Affects Versions: 1.0.0-incubating
>            Reporter: Vladimir Sitnikov
>            Assignee: Danny Chan
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 2h
>  Remaining Estimate: 0h
>
> Query optimizer can never be perfect, so it makes sense to implement hints to allow user better control the execution.
> For instance: "never merge this subquery with others" (`/+ no_merge/`), "treat those tables as leading ones" (`/*+ leading */`), etc.
> Hints would enable predictable performance and the planning time would be improved as well.



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