alamb commented on code in PR #8849:
URL: https://github.com/apache/arrow-datafusion/pull/8849#discussion_r1466311047
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datafusion/physical-expr/Cargo.toml:
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@@ -54,6 +54,7 @@ blake2 = { version = "^0.10.2", optional = true }
blake3 = { version = "1.0", optional = true }
chrono = { workspace = true }
datafusion-common = { workspace = true }
+datafusion-execution = { workspace = true }
Review Comment:
Needed to use RawTableAlloc trait
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datafusion/physical-expr/src/aggregate/count_distinct/mod.rs:
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@@ -152,6 +155,9 @@ impl AggregateExpr for DistinctCount {
Float32 => float_distinct_count_accumulator!(Float32Type),
Float64 => float_distinct_count_accumulator!(Float64Type),
+ Utf8 => Ok(Box::new(StringDistinctCountAccumulator::<i32>::new())),
Review Comment:
The key contribution in this PR is to add these specialized accumulators
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datafusion/physical-expr/src/aggregate/count_distinct/strings.rs:
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@@ -0,0 +1,487 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Specialized implementation of `COUNT DISTINCT` for `StringArray` and
`LargeStringArray`
+
+use ahash::RandomState;
+use arrow_array::cast::AsArray;
+use arrow_array::{Array, ArrayRef, GenericStringArray, OffsetSizeTrait};
+use arrow_buffer::{BufferBuilder, OffsetBuffer, ScalarBuffer};
+use datafusion_common::cast::as_list_array;
+use datafusion_common::hash_utils::create_hashes;
+use datafusion_common::utils::array_into_list_array;
+use datafusion_common::ScalarValue;
+use datafusion_execution::memory_pool::proxy::RawTableAllocExt;
+use datafusion_expr::Accumulator;
+use std::fmt::Debug;
+use std::mem;
+use std::ops::Range;
+use std::sync::Arc;
+
+#[derive(Debug)]
+pub(super) struct StringDistinctCountAccumulator<O:
OffsetSizeTrait>(SSOStringHashSet<O>);
+impl<O: OffsetSizeTrait> StringDistinctCountAccumulator<O> {
+ pub(super) fn new() -> Self {
+ Self(SSOStringHashSet::<O>::new())
+ }
+}
+
+impl<O: OffsetSizeTrait> Accumulator for StringDistinctCountAccumulator<O> {
+ fn state(&mut self) -> datafusion_common::Result<Vec<ScalarValue>> {
+ // take the state out of the string set and replace with default
+ let set = std::mem::take(&mut self.0);
+ let arr = set.into_state();
+ let list = Arc::new(array_into_list_array(arr));
+ Ok(vec![ScalarValue::List(list)])
+ }
+
+ fn update_batch(&mut self, values: &[ArrayRef]) ->
datafusion_common::Result<()> {
+ if values.is_empty() {
+ return Ok(());
+ }
+
+ self.0.insert(values[0].clone());
+
+ Ok(())
+ }
+
+ fn merge_batch(&mut self, states: &[ArrayRef]) ->
datafusion_common::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 {
+ self.0.insert(list);
+ };
+ Ok(())
+ })
+ }
+
+ fn evaluate(&mut self) -> datafusion_common::Result<ScalarValue> {
+ Ok(ScalarValue::Int64(Some(self.0.len() as i64)))
+ }
+
+ fn size(&self) -> usize {
+ // Size of accumulator
+ // + SSOStringHashSet size
+ std::mem::size_of_val(self) + self.0.size()
+ }
+}
+
+/// Maximum size of a string that can be inlined in the hash table
+const SHORT_STRING_LEN: usize = mem::size_of::<usize>();
+
+/// Entry that is stored in a `SSOStringHashSet` that represents a string
Review Comment:
This explains the core change in this PR and how things work
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