[jira] [Commented] (DRILL-4181) Improve memory limit assignment for Sort operators

["Deneche A. Hakim (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-4181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15081832#comment-15081832 ] 

Deneche A. Hakim commented on DRILL-4181:
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One more thing, currently when we run a query that uses one single fragment on a 32 core (max_width = 23) machine, the sort memory limit is still computed assuming 23 fragments will be running simultaneously.

> Improve memory limit assignment for Sort operators
> --------------------------------------------------
>
>                 Key: DRILL-4181
>                 URL: https://issues.apache.org/jira/browse/DRILL-4181
>             Project: Apache Drill
>          Issue Type: Improvement
>    Affects Versions: 1.4.0
>            Reporter: Aman Sinha
>
> Currently, the max_query_memory_per_node is divided among all the Sort operators in the query plan, regardless of whether the Sort operators are executing at the same time.  Since Sort is a blocking operator, the number of concurrent Sorts running is limited.  Thus, the Sort on both sides of a MergeJoin could be concurrently executing but a Sort that occurs above the MergeJoin cannot start until the MergeJoin produces a row which is only when both the child Sorts have produced a row. 
> Due to the conservative estimate, we have seen queries such as TPC-H Q8 with forced MergeJoin run out-of-memory even with high max_query_memory_per_node.  This query plan has 15 Sort operators and with max_width = 23,  max_query_memory_per_node = 20GB, each Sort gets only  63MB (20GB/(23*15)).    We should improve the algorithm for computing the memory limit. 



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