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