[SPARK-58928][SQL] Fix collation-aware grouping in WindowGroupLimitExec - #58195
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[SPARK-58928][SQL] Fix collation-aware grouping in WindowGroupLimitExec#58195vinodkc wants to merge 1 commit into
vinodkc wants to merge 1 commit into
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vinodkc
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Thank you @vinodkc! cc @cloud-fan to PTAL |
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What changes were proposed in this pull request?
WindowGroupLimitExec(injected by theInferWindowGroupLimitrule for rank-filter queries like WHERE rank <= N) detected partition boundaries with a raw binaryUnsafeRowcomparison (nextGroup == currentGroup).This PR makes that comparison collation-aware: it keeps the fast binary equals when all PARTITION BY keys are binary-stable, and falls back to InterpretedOrdering-based comparison when any key is not (e.g. a collated STRING), mirroring the existing pattern in
WindowEvaluatorFactory.groupEqualityCheck.Why are the changes needed?
Byte-for-byte comparison is wrong for collated strings: under
UTF8_LCASE, 'foo' and 'FOO' are equal but have different bytes, so the operator splits a single collation partition into several. The final result stays correct (the downstream WindowExec recomputes the ranking), but the limit no longer collapses collated partitions, so it forwards far more rows than needed and the optimization stops helping.Does this PR introduce any user-facing change?
No. Results are unchanged; this only restores the intended row-pruning for collated partition keys.
How was this patch tested?
Added tests in
CollationSuiteWas this patch authored or co-authored using generative AI tooling?
Yes, Generated-by: Claude Code