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Posted to github@datafusion.apache.org by "viirya (via GitHub)" <gi...@apache.org> on 2025/12/28 21:54:08 UTC
[PR] perf: improve performance of levenshtein by reusing cache buffer [datafusion]
viirya opened a new pull request, #19532:
URL: https://github.com/apache/datafusion/pull/19532
## Which issue does this PR close?
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## Rationale for this change
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## What changes are included in this PR?
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Add levenshtein_with_buffer() function that accepts a reusable cache buffer to avoid allocating a new Vec<usize> for each distance calculation.
Changes:
- Added levenshtein_with_buffer() in datafusion-common that takes a mutable
Vec<usize> buffer parameter
- Updated levenshtein function to use the optimized version with a reusable
buffer across all rows
- Applied optimization to all data types: Utf8View, Utf8, and LargeUtf8
- Added benchmark to measure performance improvements
Optimization:
- Before: Allocated new Vec<usize> cache for every row
- After: Single Vec<usize> buffer reused across all rows
Benchmark Results:
- size=1024, str_len=8: 60.6 µs → 45.9 µs (24% faster)
- size=1024, str_len=32: 615.5 µs → 598.5 µs (3% faster)
- size=4096, str_len=8: 234.7 µs → 180.5 µs (23% faster)
- size=4096, str_len=32: 2.46 ms → 2.38 ms (3% faster)
The optimization shows significant improvements for shorter strings (23-24%) where allocation overhead is more prominent relative to algorithm cost. For longer strings, the O(m×n) algorithm complexity dominates, but still shows measurable 3% improvement from eliminating per-row allocations.
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Re: [PR] perf: improve performance of levenshtein by reusing cache buffer [datafusion]
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on code in PR #19532:
URL: https://github.com/apache/datafusion/pull/19532#discussion_r2650365169
##########
datafusion/common/src/utils/mod.rs:
##########
@@ -741,6 +741,43 @@ pub mod datafusion_strsim {
generic_levenshtein(&StringWrapper(a), &StringWrapper(b))
}
+ /// Calculates the Levenshtein distance using a reusable cache buffer.
+ /// This avoids allocating a new Vec for each call, improving performance
+ /// when computing many distances.
+ ///
+ /// The `cache` buffer will be resized as needed and reused across calls.
+ pub fn levenshtein_with_buffer(a: &str, b: &str, cache: &mut Vec<usize>) -> usize {
Review Comment:
Okay, I refactored it to `generic_levenshtein_with_buffer`. Now `generic_levenshtein` calls it.
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Re: [PR] perf: improve performance of levenshtein by reusing cache buffer [datafusion]
Posted by "Jefffrey (via GitHub)" <gi...@apache.org>.
Jefffrey commented on code in PR #19532:
URL: https://github.com/apache/datafusion/pull/19532#discussion_r2650116173
##########
datafusion/common/src/utils/mod.rs:
##########
@@ -741,6 +741,43 @@ pub mod datafusion_strsim {
generic_levenshtein(&StringWrapper(a), &StringWrapper(b))
}
+ /// Calculates the Levenshtein distance using a reusable cache buffer.
+ /// This avoids allocating a new Vec for each call, improving performance
+ /// when computing many distances.
+ ///
+ /// The `cache` buffer will be resized as needed and reused across calls.
+ pub fn levenshtein_with_buffer(a: &str, b: &str, cache: &mut Vec<usize>) -> usize {
Review Comment:
I wonder if there's a way to unify this with `generic_levenshtein` to avoid duplication, something like having `generic_levenshtein` call this but creating a vec buffer at the callsite? 🤔
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Re: [PR] perf: improve performance of levenshtein by reusing cache buffer [datafusion]
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya merged PR #19532:
URL: https://github.com/apache/datafusion/pull/19532
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Re: [PR] perf: improve performance of levenshtein by reusing cache buffer [datafusion]
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on PR #19532:
URL: https://github.com/apache/datafusion/pull/19532#issuecomment-3697123264
Thanks @Jefffrey
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