dbatomic opened a new pull request, #44110:
URL: https://github.com/apache/spark/pull/44110
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Link to [JIRA](https://issues.apache.org/jira/browse/SPARK-46173).
### What changes were proposed in this pull request?
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This PR is a response to a user complaint that stated that date to string
casts are too slow if input string has many whitespace/isocontrol character as
it's prefix or sufix.
Current behaviour is that in StringToDate function we first call trimAll
function to remove any whitespace/isocontrol chars. TrimAll creates new string
and then we work against that string. This is not really needed since
StringToDate can just simply skip these characters and do all the processing in
single loop without extra allocations. Proposed fix is exactly that.
### Why are the changes needed?
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These changes should drastically improve edge case where input string in
cast to date has many whitespace as prefix/sufix.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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Extending existing tests to cover both prefix and suffix cases with
whitespaces/control chars.
The change also includes a small unit benchmark for this particular case.
Looking for feedback if we want to keep the benchmark, given that this is a
rather esoteric edge case.
The benchmark measures time needed to do 10k calls of stringToDate function
against a input strings that are in format <65k whitespace><correct_date><65
whitespace> and <correct_date><65k whitespace>. Here are the results:
| input example | prior to change | after the change |
| -------------- | ------------------ | ------------- |
| 65k whitespace prefix + 65k suffix | 3250ms | 484ms |
| 65k whitespace suffix | 1572ms | <1ms |
### Was this patch authored or co-authored using generative AI tooling?
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No
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