mingmwang commented on code in PR #4192: URL: https://github.com/apache/arrow-datafusion/pull/4192#discussion_r1021096300
########## datafusion/optimizer/src/propagate_empty_relation.rs: ########## @@ -0,0 +1,331 @@ +// 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. + +use datafusion_common::{DataFusionError, Result}; +use datafusion_expr::logical_plan::LogicalPlan; +use datafusion_expr::{EmptyRelation, JoinType, Projection}; +use std::sync::Arc; + +use crate::{utils, OptimizerConfig, OptimizerRule}; + +/// Optimization rule that bottom-up to eliminate plan by propagating empty_relation. +#[derive(Default)] +pub struct PropagateEmptyRelation; + +impl PropagateEmptyRelation { + #[allow(missing_docs)] + pub fn new() -> Self { + Self {} + } +} + +impl OptimizerRule for PropagateEmptyRelation { + fn optimize( + &self, + plan: &LogicalPlan, + optimizer_config: &mut OptimizerConfig, + ) -> Result<LogicalPlan> { + // optimize child plans first + let optimized_children_plan = + utils::optimize_children(self, plan, optimizer_config)?; + match &optimized_children_plan { + LogicalPlan::EmptyRelation(_) => Ok(optimized_children_plan), + LogicalPlan::Projection(_) + | LogicalPlan::Filter(_) + | LogicalPlan::Window(_) + | LogicalPlan::Sort(_) + | LogicalPlan::SubqueryAlias(_) + | LogicalPlan::Repartition(_) + | LogicalPlan::Limit(_) => match empty_child(&optimized_children_plan)? { + Some(empty) => Ok(empty), + None => Ok(optimized_children_plan), + }, + LogicalPlan::CrossJoin(_) => { + let (left_empty, right_empty) = binary_plan_children_is_empty(plan)?; + if left_empty || right_empty { + Ok(LogicalPlan::EmptyRelation(EmptyRelation { + produce_one_row: false, + schema: plan.schema().clone(), + })) + } else { + Ok(optimized_children_plan) + } + } + LogicalPlan::Join(join) => { + // TODO: For Join, more join type need to be careful: + // For LeftOuter/LeftSemi/LeftAnti Join, only the left side is empty, the Join result is empty. + // For LeftSemi Join, if the right side is empty, the Join result is empty. + // For LeftAnti Join, if the right side is empty, the Join result is left side(should exclude null ??). + // For RightOuter/RightSemi/RightAnti Join, only the right side is empty, the Join result is empty. + // For RightSemi Join, if the left side is empty, the Join result is empty. + // For RightAnti Join, if the left side is empty, the Join result is right side(should exclude null ??). + // For Full Join, only both sides are empty, the Join result is empty. + // For LeftOut/Full Join, if the right side is empty, the Join can be eliminated with a Projection with left side + // columns + right side columns replaced with null values. + // For RightOut/Full Join, if the left side is empty, the Join can be eliminated with a Projection with right side + // columns + left side columns replaced with null values. + if join.join_type == JoinType::Inner { + let (left_empty, right_empty) = binary_plan_children_is_empty(plan)?; + if left_empty || right_empty { + Ok(LogicalPlan::EmptyRelation(EmptyRelation { + produce_one_row: false, + schema: plan.schema().clone(), + })) + } else { + Ok(optimized_children_plan) + } + } else { + Ok(optimized_children_plan) + } + } + LogicalPlan::Union(union) => { + let (left_empty, right_empty) = binary_plan_children_is_empty(plan)?; + if left_empty && right_empty { + Ok(LogicalPlan::EmptyRelation(EmptyRelation { + produce_one_row: false, + schema: plan.schema().clone(), + })) + } else if !left_empty && right_empty { + Ok(LogicalPlan::Projection(Projection::new_from_schema( + Arc::new((**(union.inputs.get(0).unwrap())).clone()), + plan.schema().clone(), + ))) + } else if left_empty && !right_empty { + Ok(LogicalPlan::Projection(Projection::new_from_schema( + Arc::new((**(union.inputs.get(1).unwrap())).clone()), + plan.schema().clone(), + ))) + } else { + Ok(optimized_children_plan) + } + } + LogicalPlan::Aggregate(agg) => { + if !agg.group_expr.is_empty() { + match empty_child(&optimized_children_plan)? { + Some(empty) => Ok(empty), + None => Ok(optimized_children_plan), + } + } else { + Ok(optimized_children_plan) + } + } + _ => Ok(optimized_children_plan), + } + } + + fn name(&self) -> &str { + "propagate_empty_relation" + } +} + +fn binary_plan_children_is_empty(plan: &LogicalPlan) -> Result<(bool, bool)> { + let inputs = plan.inputs(); + + // all binary-plan need to deal with separately. + match inputs.len() { + 2 => { + let left = inputs.get(0).unwrap(); + let right = inputs.get(1).unwrap(); + + let left_empty = match left { + LogicalPlan::EmptyRelation(empty) => !empty.produce_one_row, + _ => false, + }; + let right_empty = match right { + LogicalPlan::EmptyRelation(empty) => !empty.produce_one_row, + _ => false, + }; + Ok((left_empty, right_empty)) + } + _ => Err(DataFusionError::Plan( + "plan just can have two child".to_string(), + )), + } +} + +fn empty_child(plan: &LogicalPlan) -> Result<Option<LogicalPlan>> { + let inputs = plan.inputs(); + + // all binary-plan need to deal with separately. + match inputs.len() { + 1 => { + let input = inputs.get(0).unwrap(); + match input { + LogicalPlan::EmptyRelation(empty) => { + if !empty.produce_one_row { + Ok(Some(LogicalPlan::EmptyRelation(EmptyRelation { + produce_one_row: false, + schema: plan.schema().clone(), + }))) + } else { + Ok(None) + } + } + _ => Ok(None), + } + } + _ => Err(DataFusionError::Plan( + "plan just can have one child".to_string(), + )), + } +} + +#[cfg(test)] +mod tests { + use crate::eliminate_filter::EliminateFilter; + use crate::test::{test_table_scan, test_table_scan_with_name}; + use datafusion_common::{Column, ScalarValue}; + use datafusion_expr::{ + binary_expr, col, lit, logical_plan::builder::LogicalPlanBuilder, Expr, JoinType, + Operator, + }; + + use super::*; + + fn assert_optimized_plan_eq(plan: &LogicalPlan, expected: &str) { + let rule = PropagateEmptyRelation::new(); + let optimized_plan = rule + .optimize(plan, &mut OptimizerConfig::new()) + .expect("failed to optimize plan"); + let formatted_plan = format!("{:?}", optimized_plan); + assert_eq!(formatted_plan, expected); + assert_eq!(plan.schema(), optimized_plan.schema()); + } + + fn assert_together_optimized_plan_eq(plan: &LogicalPlan, expected: &str) { + let optimize_one = EliminateFilter::new() + .optimize(plan, &mut OptimizerConfig::new()) + .expect("failed to optimize plan"); + let optimize_two = PropagateEmptyRelation::new() + .optimize(&optimize_one, &mut OptimizerConfig::new()) + .expect("failed to optimize plan"); + let formatted_plan = format!("{:?}", optimize_two); + assert_eq!(formatted_plan, expected); + assert_eq!(plan.schema(), optimize_two.schema()); + } + + #[test] + fn propagate_empty() -> Result<()> { + let plan = LogicalPlanBuilder::empty(false) + .filter(Expr::Literal(ScalarValue::Boolean(Some(true))))? + .limit(10, None)? + .project(vec![binary_expr(lit(1), Operator::Plus, lit(1))])? + .build()?; + + let expected = "EmptyRelation"; + assert_optimized_plan_eq(&plan, expected); + + Ok(()) + } + + #[test] + fn propagate_union_right_empty() -> Result<()> { + let table_scan = test_table_scan()?; + let left = LogicalPlanBuilder::from(table_scan).build()?; + let right_table_scan = test_table_scan_with_name("test2")?; + let right = LogicalPlanBuilder::from(right_table_scan) + .filter(Expr::Literal(ScalarValue::Boolean(Some(false))))? + .build()?; + + let plan = LogicalPlanBuilder::from(left).union(right)?.build()?; + + let expected = "Projection: a, b, c\ + \n TableScan: test"; + assert_together_optimized_plan_eq(&plan, expected); + + Ok(()) + } + + #[test] + fn propagate_union_left_empty() -> Result<()> { + let table_scan = test_table_scan()?; + let left = LogicalPlanBuilder::from(table_scan) + .filter(Expr::Literal(ScalarValue::Boolean(Some(false))))? + .build()?; + let right_table_scan = test_table_scan_with_name("test2")?; + let right = LogicalPlanBuilder::from(right_table_scan).build()?; + + let plan = LogicalPlanBuilder::from(left).union(right)?.build()?; + + let expected = "Projection: a, b, c\ + \n TableScan: test2"; + assert_together_optimized_plan_eq(&plan, expected); + + Ok(()) + } + Review Comment: Could you please add one more UT to cover the case that the union inputs have slightly different schema ? 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