distsqlrun: top k disk sorter never discards rows #31901
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A-sql-execution
Relating to SQL execution.
C-performance
Perf of queries or internals. Solution not expected to change functional behavior.
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jordanlewis
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C-performance
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cc @asubiotto |
jordanlewis
moved this from Triage
to Lower Priority Backlog
in (DEPRECATED) SQL execution
jordanlewis
added this to Triage
in [DEPRECATED] Old SQLExec board. Don't move stuff here
jordanlewis
moved this from Triage
to Lower priority backlog
in [DEPRECATED] Old SQLExec board. Don't move stuff here
asubiotto
moved this from Lower priority backlog
to [TENT] SQL Exec
in [DEPRECATED] Old SQLExec board. Don't move stuff here
|
Closing in favor of #45192 |
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The disk implementation of the top k sorter's
MaybeReplaceMaxmethod, which is supposed to sort the row into the top k rows and keep the number of saved rows at k, is currently implemented as just adding the row to the sorted disk map of rows.This is quite inefficient - I think in this case it's just falling back to global sort.
I don't think it's a huge deal - how often do we really spill top-k sorts to disk? - but this is probably something that should be fixed to prevent really bad edge case performance.
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