Aman Sinha created DRILL-4181:
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Summary: 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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