allow window aggr to be parallelizable

Author: Jiayu Liu

datafusion/src/execution/context.rs

@@ -640,6 +640,9 @@ pub struct ExecutionConfig {
     /// Should DataFusion repartition data using the aggregate keys to execute aggregates in parallel
     /// using the provided `concurrency` level
     pub repartition_aggregations: bool,
+    /// Should DataFusion repartition data using the partition keys to execute window functions in
+    /// parallel using the provided `concurrency` level
+    pub repartition_windows: bool,
 }
 
 impl Default for ExecutionConfig {
@@ -668,6 +671,7 @@ impl Default for ExecutionConfig {
             information_schema: false,
             repartition_joins: true,
             repartition_aggregations: true,
+            repartition_windows: true,
         }
     }
 }
@@ -758,11 +762,18 @@ impl ExecutionConfig {
         self.repartition_joins = enabled;
         self
     }
+
     /// Enables or disables the use of repartitioning for aggregations to improve parallelism
     pub fn with_repartition_aggregations(mut self, enabled: bool) -> Self {
         self.repartition_aggregations = enabled;
         self
     }
+
+    /// Enables or disables the use of repartitioning for window functions to improve parallelism
+    pub fn with_repartition_windows(mut self, enabled: bool) -> Self {
+        self.repartition_windows = enabled;
+        self
+    }
 }
 
 /// Holds per-execution properties and data (such as starting timestamps, etc).

datafusion/src/logical_plan/builder.rs

@@ -289,14 +289,6 @@ impl LogicalPlanBuilder {
     }
 
     /// Apply a window
-    ///
-    /// NOTE: this feature is under development and this API will be changing
-    ///
-    /// - https://github.com/apache/arrow-datafusion/issues/359 basic structure
-    /// - https://github.com/apache/arrow-datafusion/issues/298 empty over clause
-    /// - https://github.com/apache/arrow-datafusion/issues/299 with partition clause
-    /// - https://github.com/apache/arrow-datafusion/issues/360 with order by
-    /// - https://github.com/apache/arrow-datafusion/issues/361 with window frame
     pub fn window(&self, window_expr: Vec<Expr>) -> Result<Self> {
         let all_expr = window_expr.iter();
         validate_unique_names("Windows", all_expr.clone(), self.plan.schema())?;

datafusion/src/physical_plan/planner.rs

@@ -158,7 +158,7 @@ impl DefaultPhysicalPlanner {
 
                 let can_repartition = !partition_keys.is_empty()
                     && ctx_state.config.concurrency > 1
-                    && ctx_state.config.repartition_aggregations;
+                    && ctx_state.config.repartition_windows;
 
                 let input_exec = if can_repartition {
                     let partition_keys = partition_keys
@@ -221,7 +221,7 @@ impl DefaultPhysicalPlanner {
                     .map(|e| {
                         self.create_window_expr(
                             e,
-                            &logical_input_schema,
+                            logical_input_schema,
                             &physical_input_schema,
                             ctx_state,
                         )

datafusion/src/physical_plan/windows.rs

@@ -412,11 +412,14 @@ impl ExecutionPlan for WindowAggExec {
 
     /// Get the output partitioning of this plan
     fn output_partitioning(&self) -> Partitioning {
-        Partitioning::UnknownPartitioning(1)
+        // because we can have repartitioning using the partition keys
+        // this would be either 1 or more than 1 depending on the presense of
+        // repartitioning
+        self.input.output_partitioning()
     }
 
     fn required_child_distribution(&self) -> Distribution {
-        Distribution::SinglePartition
+        Distribution::UnspecifiedDistribution
     }
 
     fn with_new_children(
@@ -436,22 +439,7 @@ impl ExecutionPlan for WindowAggExec {
     }
 
     async fn execute(&self, partition: usize) -> Result<SendableRecordBatchStream> {
-        if 0 != partition {
-            return Err(DataFusionError::Internal(format!(
-                "WindowAggExec invalid partition {}",
-                partition
-            )));
-        }
-
-        // window needs to operate on a single partition currently
-        if 1 != self.input.output_partitioning().partition_count() {
-            return Err(DataFusionError::Internal(
-                "WindowAggExec requires a single input partition".to_owned(),
-            ));
-        }
-
         let input = self.input.execute(partition).await?;
-
         let stream = Box::pin(WindowAggStream::new(
             self.schema.clone(),
             self.window_expr.clone(),
@@ -591,38 +579,6 @@ mod tests {
         Ok((input, schema))
     }
 
-    #[tokio::test]
-    async fn window_function_input_partition() -> Result<()> {
-        let (input, schema) = create_test_schema(4)?;
-
-        let window_exec = Arc::new(WindowAggExec::try_new(
-            vec![create_window_expr(
-                &WindowFunction::AggregateFunction(AggregateFunction::Count),
-                "count".to_owned(),
-                &[col("c3")],
-                &[],
-                &[],
-                Some(WindowFrame::default()),
-                schema.as_ref(),
-            )?],
-            input,
-            schema.clone(),
-        )?);
-
-        let result = collect(window_exec).await;
-
-        assert!(result.is_err());
-        if let Some(DataFusionError::Internal(msg)) = result.err() {
-            assert_eq!(
-                msg,
-                "WindowAggExec requires a single input partition".to_owned()
-            );
-        } else {
-            unreachable!("Expect an internal error to happen");
-        }
-        Ok(())
-    }
-
     #[tokio::test]
     async fn window_function() -> Result<()> {
         let (input, schema) = create_test_schema(1)?;

datafusion/src/sql/utils.rs

@@ -463,7 +463,7 @@ pub(crate) fn generate_sort_key(
 /// keys.
 pub(crate) fn window_expr_common_partition_keys(
     window_exprs: &[Expr],
-) -> Result<Vec<Expr>> {
+) -> Result<&[Expr]> {
     let all_partition_keys = window_exprs
         .iter()
         .map(|expr| match expr {
@@ -474,10 +474,13 @@ pub(crate) fn window_expr_common_partition_keys(
             ))),
         })
         .collect::<Result<Vec<_>>>()?;
-    let result = all_partition_keys.iter().min_by_key(|s| s.len()).ok_or(
-        DataFusionError::Execution("No window expressions found".to_owned()),
-    )?;
-    Ok(result.to_vec())
+    let result = all_partition_keys
+        .iter()
+        .min_by_key(|s| s.len())
+        .ok_or_else(|| {
+            DataFusionError::Execution("No window expressions found".to_owned())
+        })?;
+    Ok(result)
 }
 
 /// group a slice of window expression expr by their order by expressions