Dandandan commented on code in PR #8721:
URL: https://github.com/apache/arrow-datafusion/pull/8721#discussion_r1441715955
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datafusion/physical-expr/src/aggregate/count_distinct.rs:
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@@ -192,6 +262,164 @@ impl Accumulator for DistinctCountAccumulator {
}
}
+#[derive(Debug)]
+struct NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send,
+ T::Native: Eq + Hash,
+{
+ values: HashSet<T::Native, RandomState>,
+}
+
+impl<T> NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send,
+ T::Native: Eq + Hash,
+{
+ fn new() -> Self {
+ Self {
+ values: HashSet::default(),
+ }
+ }
+}
+
+impl<T> Accumulator for NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send + Debug,
+ T::Native: Eq + Hash,
+{
+ fn state(&self) -> Result<Vec<ScalarValue>> {
+ let arr = Arc::new(PrimitiveArray::<T>::from_iter_values(
+ self.values.iter().cloned(),
+ )) as ArrayRef;
+ let list = Arc::new(array_into_list_array(arr)) as ArrayRef;
+ Ok(vec![ScalarValue::List(list)])
+ }
+
+ fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
+ if values.is_empty() {
+ return Ok(());
+ }
+
+ let arr = as_primitive_array::<T>(&values[0])?;
+ arr.iter().for_each(|value| {
+ if let Some(value) = value {
+ self.values.insert(value);
+ }
+ });
+
+ Ok(())
+ }
+
+ fn merge_batch(&mut self, states: &[ArrayRef]) -> Result<()> {
+ if states.is_empty() {
+ return Ok(());
+ }
+ assert_eq!(
+ states.len(),
+ 1,
+ "count_distinct states must be single array"
+ );
+
+ let arr = as_list_array(&states[0])?;
+ arr.iter().try_for_each(|maybe_list| {
+ if let Some(list) = maybe_list {
+ let list = as_primitive_array::<T>(&list)?;
+ self.values.extend(list.values())
+ };
+ Ok(())
+ })
+ }
+
+ fn evaluate(&self) -> Result<ScalarValue> {
+ Ok(ScalarValue::Int64(Some(self.values.len() as i64)))
+ }
+
+ fn size(&self) -> usize {
+ std::mem::size_of_val(self)
+ + std::mem::size_of_val(&self.values)
+ + (std::mem::size_of::<T::Native>() * self.values.capacity())
Review Comment:
There is also some overallocation happening (not sure how much, it might be
roughly 1.2x) to reduce collisions.
Hashes are not stored in HashSet (by default), so we shouldn't need to take
that into account.
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