alamb commented on code in PR #3009:
URL: https://github.com/apache/arrow-datafusion/pull/3009#discussion_r937097331
##########
datafusion/expr/src/accumulator.rs:
##########
@@ -44,3 +44,27 @@ pub trait Accumulator: Send + Sync + Debug {
/// returns its value based on its current state.
fn evaluate(&self) -> Result<ScalarValue>;
}
+
+#[derive(Debug)]
+pub enum AggregateState {
+ Scalar(ScalarValue),
+ Array(ArrayRef),
+}
+
+impl AggregateState {
+ pub fn as_scalar(&self) -> Result<&ScalarValue> {
+ match &self {
+ Self::Scalar(v) => Ok(v),
+ _ => Err(DataFusionError::Execution(
+ "not a scalar aggregate".to_string(),
+ )),
Review Comment:
```suggestion
_ => Err(DataFusionError::Internal(
"AggregateState is not a scalar aggregate".to_string(),
)),
```
I think marking this `Internal` might better signal to user if they hit
this, they have seen some sort of bug with DataFusion
##########
datafusion/expr/src/accumulator.rs:
##########
@@ -44,3 +44,27 @@ pub trait Accumulator: Send + Sync + Debug {
/// returns its value based on its current state.
fn evaluate(&self) -> Result<ScalarValue>;
}
+
+#[derive(Debug)]
+pub enum AggregateState {
Review Comment:
This is a very elegant idea. Can you please add docstrings to
`AggregateState` explaining what is going on?
I think it would be worth updating the docstrings in the accumulator trait
with some discussion / examples of how to use the Array state.
##########
datafusion/physical-expr/src/aggregate/count_distinct.rs:
##########
@@ -206,7 +206,10 @@ impl Accumulator for DistinctCountAccumulator {
)
});
- Ok(cols_out)
+ Ok(cols_out
+ .iter()
+ .map(|v| AggregateState::Scalar(v.clone()))
+ .collect())
Review Comment:
You can probably avoid a copy like:
```suggestion
Ok(cols_out
.into_iter()
.map(|v| AggregateState::Scalar(v))
.collect())
```
##########
datafusion/physical-expr/src/aggregate/median.rs:
##########
@@ -0,0 +1,260 @@
+// 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.
+
+//! # Median
+
+use crate::expressions::format_state_name;
+use crate::{AggregateExpr, PhysicalExpr};
+use arrow::array::{
+ Array, ArrayRef, Float32Array, Float64Array, Int16Array, Int32Array,
Int64Array,
+ Int8Array, PrimitiveArray, PrimitiveBuilder, UInt16Array, UInt32Array,
UInt64Array,
+ UInt8Array,
+};
+use arrow::compute::sort;
+use arrow::datatypes::{ArrowPrimitiveType, DataType, Field};
+use datafusion_common::{DataFusionError, Result, ScalarValue};
+use datafusion_expr::{Accumulator, AggregateState};
+use std::any::Any;
+use std::sync::Arc;
+
+/// MEDIAN aggregate expression. This uses a lot of memory because all values
need to be
+/// stored in memory before a result can be computed. If an approximation is
sufficient
Review Comment:
I wonder if it is worth (perhaps as a follow on PR) putting a cap on the
number of values DataFusion will try to buffer to compute median and throw a
runtime error if that number is exceeded 🤔 That way we could avoid OOM kills
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