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https://issues.apache.org/jira/browse/IMPALA-10099?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Shant Hovsepian closed IMPALA-10099.
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> Push down DISTINCT aggregation for EXCEPT/INTERSECT
> ---------------------------------------------------
>
> Key: IMPALA-10099
> URL: https://issues.apache.org/jira/browse/IMPALA-10099
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Shant Hovsepian
> Assignee: Shant Hovsepian
> Priority: Major
> Fix For: Impala 4.0
>
>
> The implementation of SetOperations for EXCEPT/INTERSECT in IMPALA-9943
> produced query rewrites that would apply DISTINCT aggregation after exchanges
> for distributed plans. In case where the query can be directly rewritten to
> apply the DISTINCT to the set operation operands would result in better
> performance for most large queries.
> This should help the performance TPC-DS Q14 which does an INTERSECT of
> queries with large result sets that contain many duplicates.
> In general it would better to have DISTINCT move around optimization phase
> during planning which would handle this case as well as many others.
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