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GH-55281: [C++][Gandiva] Release arena memory per row when no function returns a string - #55282
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…ena growth levenshtein returns int32 but uses arena memory, so the per-row arena release is never emitted for it. This test fails until that is fixed.
…shtein Add a kUsesArena flag, set it for levenshtein, and release the arena per row for flagged functions.
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…d string functions An external function that takes the context and arena scratch but returns int32 still keeps its memory until the end of the batch. This test fails until that is fixed.
…unction with context Use NeedsContext() instead of the kUsesArena flag, and skip the reset call when the row did not allocate.
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October 27, 2026 16:08
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Rationale for this change
Gandiva releases the arena per row only if some function returns a string. Functions that take the context but return other types (
levenshtein, external functions) keep their arena memory until the end of the batch. See #55281.What changes are included in this PR?
kNeedsContext. A function without the context cannot reach the arena.For someone who wants to follow along:
Results
Memory per batch, 262,144 rows:
levenshteinPerformance, ns/row (Apple M3, 1M rows):
divideint64divideint32castVARCHAR(s, 8)Are these changes tested?
Yes, via new targeted test with commit history showing them being effective
Considered, not chosen
kUsesArenaflag on arena users (commit 2): manual. A missed flag leaks silently.divide2x slower (0.50 to 1.07 ns/row).divideint64 3x slower (0.53 to 1.49 ns/row) on Apple M3. Any per-row store costs about 1 ns there.Are there any user-facing changes?
No.
Was AI used for this PR?
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