QinXi-ai commented on code in PR #25988:
URL: https://github.com/apache/datafusion/pull/25988#discussion_r4500465393
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datafusion/optimizer/src/single_distinct_to_groupby.rs:
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@@ -154,12 +155,41 @@ fn is_single_distinct_agg(
if aggregate_count != aggr_expr.len() || fields_set.len() != 1 {
return Ok(false);
}
+ // With one target partition, a native GroupsAccumulator avoids building an
+ // extra aggregate with a row per (group, distinct value) pair. With
multiple
+ // partitions, the rewrite also distributes deduplication by both keys;
+ // keeping DISTINCT instead repartitions lists of values by group and
merges
+ // them in the final accumulator. That can concentrate work on a few
groups.
+ // Native accumulator support alone does not establish that this is
cheaper.
+ if use_native_grouped_distinct
+ && distinct_aggs.len() == aggregate_count
+ && all_have_groups_accumulators(&distinct_aggs, input_schema)?
+ {
+ return Ok(false);
+ }
if has_count_rollup && !rewrite_pays_for_count(&distinct_aggs,
input_schema)? {
return Ok(false);
}
Ok(true)
}
+fn all_have_groups_accumulators(
Review Comment:
Done, both checks now share the type lookup through
`distinct_groups_support`. I also added the opt-in exception to the rule's doc
comment.
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