fix: reduce memory allocation overhead during partial aggregation ear…#22165
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ariel-miculas wants to merge 1 commit into
Open
fix: reduce memory allocation overhead during partial aggregation ear…#22165ariel-miculas wants to merge 1 commit into
ariel-miculas wants to merge 1 commit into
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…ly emit When the partial hash aggregation (with GroupOrdering::None) cannot reserve additional memory, it calls self.emit(EmitTo::First(n), where n is the largest integer multiple of self.batch_size, meaning it's close to the length of group_values. Using drain + collect leads to an additional copy of all these n values, since collect allocates a new Vec and drain doesn't modify the original vector's capacity. To avoid copying the largest allocation, choose a strategy which always allocates the minimum between n and remaining. Fixes apache#22164
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…ly emit
Which issue does this PR close?
Rationale for this change
When the partial hash aggregation (with GroupOrdering::None) cannot reserve additional memory, it calls self.emit(EmitTo::First(n), where n is the largest integer multiple of self.batch_size, meaning it's close to the length of group_values. Using drain + collect leads to an additional copy of all these n values, since collect allocates a new Vec and drain doesn't modify the original vector's capacity. To avoid copying the largest allocation, choose a strategy which always allocates the minimum between n and remaining.
What changes are included in this PR?
Are these changes tested?
Yes, added unit tests
Are there any user-facing changes?
No