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https://issues.apache.org/jira/browse/IMPALA-7843?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong resolved IMPALA-7843.
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Resolution: Won't Do
I don't think this is viable to implement.
> 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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