[8.18] Avoid O(N^2) in VALUES with ordinals grouping (#130576) #130778
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Using the VALUES aggregator with ordinals grouping led to accidental quadratic complexity. Queries like FROM .. | STATS ... VALUES(field) ... BY keyword-field are affected by this performance issue. This change caches a sorted structure - previously used to fix a similar O(N^2) problem when emitting the output block - during the merging phase of the OrdinalGroupingOperator. (cherry picked from commit 59df1bf) # Conflicts: # benchmarks/src/main/java/org/elasticsearch/benchmark/compute/operator/ValuesAggregatorBenchmark.java # x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/aggregation/ValuesBytesRefAggregator.java # x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/aggregation/ValuesDoubleAggregator.java # x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/aggregation/ValuesFloatAggregator.java # x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/aggregation/ValuesIntAggregator.java # x-pack/plugin/esql/compute/src/main/generated-src/org/elasticsearch/compute/aggregation/ValuesLongAggregator.java # x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/aggregation/ValuesBytesRefAggregators.java # x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/aggregation/X-ValuesAggregator.java.st
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