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[parquet] Avoid a clone while resolving the read strategy #9056

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Merged
alamb merged 3 commits into from
Jan 5, 2026
+13 −10
Merged

[parquet] Avoid a clone while resolving the read strategy #9056

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e070bdc
Avoid a clone while resolving the read plan
alamb Dec 28, 2025
fe10c50
Implement suggestions from @hhhizzz
alamb Dec 29, 2025
ef2a9a2
Merge branch 'main' into alamb/no_clone
alamb Jan 5, 2026
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14 changes: 4 additions & 10 deletions parquet/src/arrow/arrow_reader/read_plan.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -110,19 +110,13 @@ impl ReadPlanBuilder {
None => return RowSelectionStrategy::Selectors,
};

let trimmed = selection.clone().trim();
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@alamb alamb Dec 28, 2025

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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

let selectors: Vec<RowSelector> = trimmed.into();
if selectors.is_empty() {
return RowSelectionStrategy::Mask;
}

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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@hhhizzz hhhizzz Dec 29, 2025

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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_count is too long, effective_count could sound better.
  • Using fold to 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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@alamb alamb Dec 29, 2025

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This is a great idea -- done in fe10c50

let total_rows: usize = selection.iter().map(|s| s.row_count).sum();
if non_empty_selector_count == 0 {
return RowSelectionStrategy::Mask;
}

if total_rows < selector_count.saturating_mul(threshold) {
if total_rows < non_empty_selector_count.saturating_mul(threshold) {
RowSelectionStrategy::Mask
} else {
RowSelectionStrategy::Selectors
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