TinyMurky commented on code in PR #25158:
URL: https://github.com/apache/datafusion/pull/25158#discussion_r3995637305
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datafusion/physical-plan/src/aggregates/single_stream.rs:
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@@ -449,6 +454,27 @@ impl SingleHashAggregateStream {
return Self::break_with_err(e);
}
+ // Soft limit optimization:
+ //
+ // Stop reading input once the in-memory table contains enough
distinct
+ // groups to satisfy the soft limit.
+ //
+ // When a limit is present, AggregateExec routes only
unordered,
+ // unfiltered DISTINCT aggregates to this stream.
+ //
+ // With no aggregate expressions, additional input can only
match existing
+ // groups or add new ones; it cannot change any existing
group's output.
+ // Since there is no ordering requirement and we already have
enough
+ // distinct groups, we can finish reading as if the input were
exhausted.
+ //
+ // Reuse the input-exhausted transition to merge any existing
spills
+ // before producing output. The downstream limit operator
enforces
+ // the exact output row count.
+ if self.hit_soft_group_limit(&hash_table) {
Review Comment:
I added the skip of spilling.
https://github.com/apache/datafusion/blob/e92aee75ea5bf774d0dbd6be648849a124c7797e/datafusion/physical-plan/src/aggregates/single_stream.rs#L485-L498
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