[parquet] Avoid a clone while resolving the read strategy #9056
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alamb
changed the title
alamb
commented
Dec 28, 2025
| None => return RowSelectionStrategy::Selectors, | ||
| }; | ||
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| let trimmed = selection.clone().trim(); |
Contributor
Author
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this clone shows up in the traces for some of the clickbench queries. I think this is because there are 9000 selectors for these queries
hhhizzz
reviewed
Dec 29, 2025
| let total_rows: usize = selectors.iter().map(|s| s.row_count).sum(); | ||
| let selector_count = selectors.len(); | ||
| if selector_count == 0 { | ||
| let non_empty_selector_count = selection.iter().filter(|s| s.row_count > 0).count(); |
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Good improvement! I didn’t notice this in my benchmarks, likely because the dataset was too small.
Small suggestion:
non_empty_selector_countis too long,effective_countcould sound better.- Using
foldto replace 2 seperate iteration might be better.
let (total_rows, effective_count) = selection.iter()
.fold((0, 0), |(rows, count), s| {
if s.row_count > 0 {
(rows + s.row_count, count + 1)
} else {
(rows, count)
}
});
if effective_count == 0 {
return RowSelectionStrategy::Mask;
}
if total_rows < effective_count.saturating_mul(threshold) {
RowSelectionStrategy::Mask
} else {
RowSelectionStrategy::Selectors
}
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🤖 |
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🤖: Benchmark completed Details
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Contributor
Author
|
run benchmark arrow_reader_row_filter |
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🤖 |
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🤖: Benchmark completed Details
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Contributor
Author
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@hhhizzz do you think this PR is ready to merge? |
Contributor
Yeah, I think its ready to merge. |
Contributor
Author
Thank you for the review ❤️ |
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Which issue does this PR close?
Rationale for this change
While working on apache/datafusion#19477, and profiling ClickBench q7, I noticed that the RowSelectors was being cloned to resolve the strategy -- for a large number of selections this is expensive and shows up in the traces
We should change the code to avoid cloning the RowSelectors when resolving the strategy.
Changes
Don't clone / allocate while resolving the strategy.
I don't expect this to have a massive impact, but it did show up in the profile
FYI @hhhizzz -- perhaps you could review this PR
Are these changes tested?
Yes by CI
Are there any user-facing changes?
small performance improvement