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Refactor size estimation of Hashset into a function #8779

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Refactor size estimation of Hashset into a function #8779

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ac628d9
estimation into function
yyy1000 Jan 7, 2024
0ec8a57
Update datafusion/physical-expr/src/aggregate/count_distinct.rs
yyy1000 Jan 8, 2024
22f885a
Update datafusion/physical-expr/src/aggregate/count_distinct.rs
yyy1000 Jan 8, 2024
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15 changes: 9 additions & 6 deletions datafusion/physical-expr/src/aggregate/count_distinct.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,13 @@ macro_rules! float_distinct_count_accumulator {
}};
}

/// Returns the estimated number of hashbrown hashtables is likely to come up again
fn estimated_buckets<T>(hashset: &HashSet<T, RandomState>) -> usize {
let estimated_buckets =
(hashset.len().checked_mul(8).unwrap_or(usize::MAX) / 7).next_power_of_two();
estimated_buckets
}

impl AggregateExpr for DistinctCount {
/// Return a reference to Any that can be used for downcasting
fn as_any(&self) -> &dyn Any {
Expand Down Expand Up @@ -336,9 +343,7 @@ where
}

fn size(&self) -> usize {
let estimated_buckets = (self.values.len().checked_mul(8).unwrap_or(usize::MAX)
/ 7)
.next_power_of_two();
let estimated_buckets = estimated_buckets(&self.values);

// Size of accumulator
// + size of entry * number of buckets
Expand Down Expand Up @@ -423,9 +428,7 @@ where
}

fn size(&self) -> usize {
let estimated_buckets = (self.values.len().checked_mul(8).unwrap_or(usize::MAX)
/ 7)
.next_power_of_two();
let estimated_buckets = estimated_buckets(&self.values);

// Size of accumulator
// + size of entry * number of buckets
Expand Down