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When we write complex queries final physical plan may include SortExecs that are unnecessary. Consider the query below
SELECT count(*) as global_count FROM
(SELECT count(*), c1
FROM aggregate_test_100
WHERE c13 != 'C2GT5KVyOPZpgKVl110TyZO0NcJ434'
GROUP BY c1
ORDER BY c1 ) AS aIts physical plan is as follows
"ProjectionExec: expr=[COUNT(UInt8(1))@0 as global_count]",
" AggregateExec: mode=Final, gby=[], aggr=[COUNT(UInt8(1))]",
" CoalescePartitionsExec",
" AggregateExec: mode=Partial, gby=[], aggr=[COUNT(UInt8(1))]",
" RepartitionExec: partitioning=RoundRobinBatch(2)",
" SortExec: [c1@0 ASC NULLS LAST]",
" CoalescePartitionsExec",
" AggregateExec: mode=FinalPartitioned, gby=[c1@0 as c1], aggr=[COUNT(UInt8(1))]",
" CoalesceBatchesExec: target_batch_size=4096",
" RepartitionExec: partitioning=Hash([Column { name: \"c1\", index: 0 }], 2)",
" AggregateExec: mode=Partial, gby=[c1@0 as c1], aggr=[COUNT(UInt8(1))]",
" CoalesceBatchesExec: target_batch_size=4096",
" FilterExec: c13@1 != C2GT5KVyOPZpgKVl110TyZO0NcJ434",
" RepartitionExec: partitioning=RoundRobinBatch(2)",SortExec in the physical plan is unnecessary because following executor (RepartitionExec) doesn't require input ordering and doesn't maintain input ordering either. Hence even if we sort before this executor, the executor will overwrite sorting and ordering will be lost. Add support for removing SortExec in these scenarios.
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We can traverse physical plan bottom up and if ordering information introduced by SortExec is overwritten by another executor without using ordering information itself. We can remove corresponding SortExec from the plan. Additionally, some executors can produce their result with reversed order also. Consider the query below
SELECT count(*) OVER(ORDER BY c9 ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING) as cnt1,
count(*) OVER(ORDER BY c9 DESC ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING) as cnt2
FROM aggregate_test_100whose physical plan is
"ProjectionExec: expr=[COUNT(UInt8(1)) ORDER BY [aggregate_test_100.c9 ASC NULLS LAST] ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING@0 as cnt1, COUNT(UInt8(1)) ORDER BY [aggregate_test_100.c9 DESC NULLS FIRST] ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING@1 as cnt2]",
" WindowAggExec: wdw=[COUNT(UInt8(1)): Ok(Field { name: \"COUNT(UInt8(1))\", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), frame: WindowFrame { units: Rows, start_bound: Preceding(UInt64(3)), end_bound: Following(UInt64(5)) }]",
" SortExec: [c9@1 ASC NULLS LAST]",
" WindowAggExec: wdw=[COUNT(UInt8(1)): Ok(Field { name: \"COUNT(UInt8(1))\", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), frame: WindowFrame { units: Rows, start_bound: Preceding(UInt64(3)), end_bound: Following(UInt64(5)) }]",
" SortExec: [c9@0 DESC]",
Its physical plan include second Sorting to reverse ordering. However, count aggregator can produce its result with reverse order also. By exploiting this property we can turn above physical plan into the below
"ProjectionExec: expr=[COUNT(UInt8(1)) ORDER BY [aggregate_test_100.c9 ASC NULLS LAST] ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING@0 as cnt1, COUNT(UInt8(1)) ORDER BY [aggregate_test_100.c9 DESC NULLS FIRST] ROWS BETWEEN 3 PRECEDING AND 5 FOLLOWING@1 as cnt2]",
" WindowAggExec: wdw=[COUNT(UInt8(1)): Ok(Field { name: \"COUNT(UInt8(1))\", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), frame: WindowFrame { units: Rows, start_bound: Preceding(UInt64(3)), end_bound: Following(UInt64(5)) }]",
" WindowAggExec: wdw=[COUNT(UInt8(1)): Ok(Field { name: \"COUNT(UInt8(1))\", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), frame: WindowFrame { units: Rows, start_bound: Preceding(UInt64(3)), end_bound: Following(UInt64(5)) }]",
" SortExec: [c9@0 DESC]",
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