viirya opened a new pull request, #19555:
URL: https://github.com/apache/datafusion/pull/19555
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## Rationale for this change
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## What changes are included in this PR?
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Replace per-row Vec<char> allocation with a reusable buffer in trim
functions (ltrim, rtrim, btrim).
The previous implementation allocated a Vec<char> for the pattern on every
row, which was inefficient. This optimization introduces a pattern_buf that is
allocated once and reused across all rows by clearing and refilling it.
Changes:
- Refactored general_trim to pass TrimType directly instead of closures
- Created apply_trim helper function that accepts a mutable pattern buffer
- Updated string_view_trim and string_trim to allocate pattern_buf once
- Buffer is cleared and reused for each row to avoid repeated allocations
Benchmark results for ltrim (size=1024):
- INPUT LEN <= 12, string_view: 21.484 µs -> 13.243 µs (38.4% faster, 1.6x
speedup)
- INPUT LEN <= 12, string: 21.540 µs -> 14.051 µs (34.8% faster, 1.5x
speedup)
- INPUT LEN > 12, OUTPUT LEN > 12, string_view: 21.951 µs -> 13.325 µs
(39.3% faster, 1.6x speedup)
- INPUT LEN > 12, OUTPUT LEN > 12, string: 24.328 µs -> 16.844 µs (30.8%
faster, 1.4x speedup)
- INPUT LEN > 12, OUTPUT LEN <= 12, string_view: 87.967 µs -> 77.016 µs
(12.4% faster)
Benchmark results for ltrim (size=4096):
- INPUT LEN <= 12, string_view: 85.626 µs -> 51.478 µs (39.9% faster, 1.7x
speedup)
- INPUT LEN <= 12, string: 84.011 µs -> 54.774 µs (34.8% faster, 1.5x
speedup)
- INPUT LEN > 12, OUTPUT LEN > 12, string_view: 85.964 µs -> 51.825 µs
(39.7% faster, 1.7x speedup)
- INPUT LEN > 12, OUTPUT LEN > 12, string: 102.42 µs -> 74.097 µs (27.7%
faster, 1.4x speedup)
The optimization shows consistent 28-40% improvement across most workloads
by eliminating per-row Vec allocations. This applies to all trim variants
(ltrim, rtrim, btrim) as they share the same underlying implementation.
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