Fix O(n^2) performance bug in uniqArr; avoid duplicate keyF evaluations#575
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stephenamar-db merged 1 commit intodatabricks:masterfrom Dec 22, 2025
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The previous implementation called ArrayBuilder.result() inside the loop, which creates a new array copy on each iteration, resulting in O(n²) behavior. This fix tracks lastAddedKey separately to compare against the previous element's key without rebuilding the array. Also uses a while loop instead of foreach to avoid closure allocation overhead. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
He-Pin
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Dec 22, 2025
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@JoshRosen Thanks, I think we may need use Ai agent to do a detailed review around the current implementation before we cut 1.0.0 |
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This PR implements two performance optimizations in
uniqueArr:out.result()on every loop iteration, resulting in copying of anO(n)sized array on each loop iteration. We can avoid this by keeping a reference to the last output element.keyFevaluation for the last element of the output array; the new code callskeyFexactly once per element by maintaining alastAddedKeyvariable during the loop.Claude (Opus 4.5) spotted the O(n^2) bug and designed that part of the fix. I spotted the duplicate keyF evaluation and suggested this fix (plus the switch to a
whileloop).