coderfender commented on code in PR #21456:
URL: https://github.com/apache/datafusion/pull/21456#discussion_r3061010490
##########
datafusion/functions-aggregate-common/src/aggregate/count_distinct/native.rs:
##########
@@ -165,3 +165,354 @@ impl<T: ArrowPrimitiveType + Debug> Accumulator for
FloatDistinctCountAccumulato
size_of_val(self) + self.values.size()
}
}
+
+/// Optimized COUNT DISTINCT accumulator for u8 using a bool array.
+/// Uses 256 bytes to track all possible u8 values.
+#[derive(Debug)]
+pub struct BoolArray256DistinctCountAccumulator {
+ seen: Box<[bool; 256]>,
Review Comment:
Results using `MutableBuffer` : (slower than directly using bitmap)
```
group bitmap_count_distinct
bitmap_count_distinct_mutable_buffer main
----- ---------------------
------------------------------------ ---- 6.2±0.22µs ?
?/sec
count_distinct i16 bitmap 1.03 3.1±0.14µs ?
?/sec 1.00 3.0±0.02µs ? ?/sec 26.16 77.9±3.43µs ?
?/sec
count_distinct i64 80% distinct 1.03 48.2±0.44µs ?
?/sec 1.00 47.0±0.40µs ? ?/sec 1.02 48.0±1.49µs ?
?/sec
count_distinct i64 99% distinct 1.02 48.3±0.46µs ?
?/sec 1.00 47.2±0.92µs ? ?/sec 1.02 48.3±2.14µs ?
?/sec
count_distinct i8 bitmap 1.00 2.9±0.43µs ?
?/sec 1.37 3.9±0.06µs ? ?/sec 5.75 16.4±0.26µs ?
?/sec
count_distinct u16 bitmap 1.06 3.2±0.30µs ?
?/sec 1.00 3.0±0.16µs ? ?/sec 25.58 77.7±1.82µs ?
?/sec
count_distinct u8 bitmap 1.00 2.1±0.03µs ?
?/sec 1.90 3.9±0.08µs ? ?/sec 8.14
```
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