Dandandan commented on code in PR #15324:
URL: https://github.com/apache/datafusion/pull/15324#discussion_r2005787338
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datafusion/functions-aggregate/src/count.rs:
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@@ -752,10 +761,245 @@ impl Accumulator for DistinctCountAccumulator {
}
}
+/// GroupsAccumulator for COUNT DISTINCT operations
+#[derive(Debug)]
+pub struct DistinctCountGroupsAccumulator {
+ /// One HashSet per group to track distinct values
+ distinct_sets: Vec<HashSet<ScalarValue, RandomState>>,
Review Comment:
I wonder if a single `HashSet<(u64, ScalarValue), RandomState>>` (i.e. also
index by group id rather than create a new `HashSet` per group) might be
faster? It will use less memory and intuitively should be more cache friendly.
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