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Posted to issues-all@impala.apache.org by "Tim Armstrong (JIRA)" <ji...@apache.org> on 2019/01/26 00:14:00 UTC
[jira] [Commented] (IMPALA-7843) MT_DOP should be configurable per
subquery
[ https://issues.apache.org/jira/browse/IMPALA-7843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16752838#comment-16752838 ]
Tim Armstrong commented on IMPALA-7843:
---------------------------------------
[~jonapgar] I'm looking at adding an experimental flag to enable mt_dop for all queries: IMPALA-8097. It will initially be a "use at your own risk" flag will come with a bunch of caveats since it will be missing various optimisations, tuning, etc.
But this might be of interest to you - it would of course be good to get feedback on it.
> MT_DOP should be configurable per subquery
> ------------------------------------------
>
> Key: IMPALA-7843
> URL: https://issues.apache.org/jira/browse/IMPALA-7843
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Jon Apgar
> Priority: Major
>
> MT_DOP > 0 will cause queries with JOIN statements to fail, however the *subqueries* within the main query _might_ otherwise have been able to run successfully with MT_DOP > 0.
> A use-case for subqueries may be to limit the size of complex joins or eliminate redundant aggregation in the outer query, By allowing MT_DOP > 0 on subqueries you could significantly speed up the entire query.
> MT_DOP is not the only session variable which may be effectively configured per subquery. Perhaps there should be a way of specifying applicable variables within the select statement of a query.
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