Improve performance of distinct aggregations #21907
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Extract the logic to determine whether the direct distinct aggregation applicability, which can be reused in multiple optimiser rules.
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The rule replaces `OptimizeMixedDistinctAggregations`, and adds support for multiple distinct aggregations.
Also rename corresponding config property optimizer.mark-distinct-strategy to optimizer.distinct-aggregations-strategy and values to NONE -> SINGLE_STEP and ALWAYS -> MARK_DISTINCT
Replace optimizer.optimize-mixed-distinct-aggregations with a new optimizer.distinct-aggregations-strategy `pre_aggregate`
Use estimated aggregation source NDV and the number of grouping keys to decide if pre-aggregate strategy should be used for a given aggregation
lukasz-stec
approved these changes
May 21, 2024
| { | ||
| return session.getSystemProperty(MARK_DISTINCT_STRATEGY, MarkDistinctStrategy.class); | ||
| return session.getSystemProperty(DISTINCT_AGGREGATIONS_STRATEGY, DistinctAggregationsStrategy.class); |
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you should merge this commit with the commit that re-adds the MARK_DISTINCT_STRATEGY propertry
| @@ -683,6 +683,9 @@ public PlanOptimizers( | |||
| new RemoveRedundantIdentityProjections(), | |||
| new PushAggregationThroughOuterJoin(), | |||
| new ReplaceRedundantJoinWithSource(), // Run this after PredicatePushDown optimizer as it inlines filter constants | |||
| new DistinctAggregationToGroupBy(plannerContext), // Run this after aggregation pushdown so that multiple distinct aggregations can be pushed into a connector | |||
| // It also is run before MultipleDistinctAggregationToMarkDistinct to take precedence f enabled | |||
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nit: typo should be precedence if enabled
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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_STEPComputes distinct aggregations in single-step without any pre-aggregations.This strategy will perform poorly if the number of distinct grouping keys is small.
MARK_DISTINCTusesMarkDistinctfor multiple distinct aggregationsor for mix of distinct and non-distinct aggregations.
PRE_AGGREGATEComputes distinct aggregations using a combination of aggregationand pre-aggregation steps.
AUTOMATICchooses 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
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