adriangb commented on code in PR #17606:
URL: https://github.com/apache/datafusion/pull/17606#discussion_r2354278704
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datafusion/functions-aggregate/src/count.rs:
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@@ -746,12 +746,25 @@ fn null_count_for_multiple_cols(values: &[ArrayRef]) ->
usize {
/// more efficient such as [`PrimitiveDistinctCountAccumulator`] and
/// [`BytesDistinctCountAccumulator`]
#[derive(Debug)]
-struct DistinctCountAccumulator {
+pub struct DistinctCountAccumulator {
values: HashSet<ScalarValue, RandomState>,
Review Comment:
I don't know much about "perfect join" but I worry that tracking distinct
values is considerable overhead. Do we do it *only* when we know we will 100%
for sure be able to do a "perfect join"? If the cardinality is high or other
pathological cases, is it still always faster to track the distinct values?
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