Dandandan commented on code in PR #21456:
URL: https://github.com/apache/datafusion/pull/21456#discussion_r3060778380
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datafusion/functions-aggregate-common/src/aggregate/count_distinct/native.rs:
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@@ -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:
For small arrays this might not be necessarily faster (as it fits in L1
cache) - perhaps only if you can use instructions like popcount etc.?
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