Improve performance of distinct aggregations #21907
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Description
Improve performance of distinct aggregations by defining additional strategies based on source properties (for example, NDV).
The strategy to use for multiple distinct aggregations.
SINGLE_STEP
Computes distinct aggregations in single-step without any pre-aggregations.This strategy will perform poorly if the number of distinct grouping keys is small.
MARK_DISTINCT
usesMarkDistinct
for multiple distinct aggregationsor for mix of distinct and non-distinct aggregations.
PRE_AGGREGATE
Computes distinct aggregations using a combination of aggregationand pre-aggregation steps.
AUTOMATIC
chooses the strategy automatically.Single-step strategy is preferred. However, for cases with limited concurrency due to
a small number of distinct grouping keys, it will choose an alternative strategy
based on input data statistics.
Additional context and related issues
Release notes
( ) This is not user-visible or is docs only, and no release notes are required.
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( ) Release notes are required, with the following suggested text: