ORCA: Fix window function cost model producing zero local cost when no ORDER BY#1573
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yjhjstz merged 1 commit intoapache:mainfrom Feb 24, 2026
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ORCA: Fix window function cost model producing zero local cost when no ORDER BY#1573yjhjstz merged 1 commit intoapache:mainfrom
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Pull request overview
This PR fixes a bug in the ORCA cost model where window functions without an ORDER BY clause had zero local cost, causing the optimizer to incorrectly prefer non-hash variants due to tie-breaking by insertion order.
Changes:
- Modified window function cost calculations to use
max(ulSortCols, 1)ensuring non-zero cost even without ORDER BY - Fixed function header comment for CostHashSequenceProject (previously incorrectly labeled as CostSequenceProject)
- Added explanatory comments documenting the rationale for the minimum cost factor
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leborchuk
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ulSortCols by default is 0 and SQL could not have ORDER BY in WINDOW CLAUSE, it's unusual but make sense in some cases. For those queries we produce zero cost bacause of default ulSortCols value.
Need to be fixed, LGTM
reshke
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Feb 24, 2026
…o ORDER BY When a window function has no ORDER BY clause (empty Order Spec), ulSortCols is 0, causing the local cost of SequenceProject operators to be zero. This makes CostHashSequenceProject and CPhysicalSequenceProject have identical costs. Fix by using max(ulSortCols, 1) so the window function evaluation cost is never zero.
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…o ORDER BY (#1573) When a window function has no ORDER BY clause (empty Order Spec), ulSortCols is 0, causing the local cost of SequenceProject operators to be zero. This makes CostHashSequenceProject and CPhysicalSequenceProject have identical costs. Fix by using max(ulSortCols, 1) so the window function evaluation cost is never zero.
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…o ORDER BY (apache#1573) When a window function has no ORDER BY clause (empty Order Spec), ulSortCols is 0, causing the local cost of SequenceProject operators to be zero. This makes CostHashSequenceProject and CPhysicalSequenceProject have identical costs. Fix by using max(ulSortCols, 1) so the window function evaluation cost is never zero.
reshke
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…o ORDER BY (apache#1573) When a window function has no ORDER BY clause (empty Order Spec), ulSortCols is 0, causing the local cost of SequenceProject operators to be zero. This makes CostHashSequenceProject and CPhysicalSequenceProject have identical costs. Fix by using max(ulSortCols, 1) so the window function evaluation cost is never zero.
reshke
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Mar 12, 2026
…o ORDER BY (#1573) When a window function has no ORDER BY clause (empty Order Spec), ulSortCols is 0, causing the local cost of SequenceProject operators to be zero. This makes CostHashSequenceProject and CPhysicalSequenceProject have identical costs. Fix by using max(ulSortCols, 1) so the window function evaluation cost is never zero.
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When a window function has no ORDER BY clause (empty Order Spec),
ulSortCols is 0, causing the local cost of SequenceProject operators
to be zero. This makes CostHashSequenceProject and
CPhysicalSequenceProject have identical costs.
Fixes #ISSUE_Number
What does this PR do?
Type of Change
Breaking Changes
Test Plan
make installcheckmake -C src/test installcheck-cbdb-parallelImpact
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