neilconway opened a new pull request, #21119:
URL: https://github.com/apache/datafusion/pull/21119
## Which issue does this PR close?
- Closes #21117.
- Closes #21118 .
## Rationale for this change
`split_part` currently accepts `Utf8View` but always returns `Utf8`. When
given `Utf8View` input, it should instead return `Utf8View` output.
While we're at it, optimize `split_part` for single-character delimiters
(the common case): `str::split(&str)` is significantly slower than
`str::split(char)` for single-character ASCII delimiters, because the former
uses a general string matching algorithm but the latter uses `memchr::memchr`.
Benchmark results:
- `utf8_single_char/pos_first`: 141 µs → 106 µs (-25%)
- `utf8_single_char/pos_middle`: 392 µs → 368 µs (-6%)
- `utf8_single_char/pos_negative`: 151 µs → 116 µs (-24%)
- `utf8_multi_char/pos_middle`: 375 µs → 362 µs (-2%, noise; this path is
unchanged)
- `utf8view_single_char/pos_first`: 143 µs → 111 µs (-22%)
- `utf8view_long_parts/pos_middle`: 1022 µs → 469 µs (-54%)
## What changes are included in this PR?
* Revise `split_part` benchmarks to reduce redundancy and improve `Utf8View`
coverage
* Support `Utf8View` -> `Utf8View` in `split_part`
* Refactor `split_part` to cleanup some redundant code
* Optimize `split_part` for single-character delimiters
* Add SLT test coverage for `split_part` with `Utf8View` input
## Are these changes tested?
Yes. New tests and benchmarks added.
## Are there any user-facing changes?
No.
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