ozankabak commented on code in PR #4691: URL: https://github.com/apache/arrow-datafusion/pull/4691#discussion_r1056439006
########## datafusion/core/src/physical_optimizer/remove_unnecessary_sorts.rs: ########## @@ -0,0 +1,887 @@ +// 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. + +//! RemoveUnnecessarySorts optimizer rule inspects SortExec's in the given +//! physical plan and removes the ones it can prove unnecessary. The rule can +//! work on valid *and* invalid physical plans with respect to sorting +//! requirements, but always produces a valid physical plan in this sense. +//! +//! A non-realistic but easy to follow example: Assume that we somehow get the fragment +//! "SortExec: [nullable_col@0 ASC]", +//! " SortExec: [non_nullable_col@1 ASC]", +//! in the physical plan. The first sort is unnecessary since its result is overwritten +//! by another SortExec. Therefore, this rule removes it from the physical plan. +use crate::error::Result; +use crate::physical_optimizer::utils::{ + add_sort_above_child, ordering_satisfy, ordering_satisfy_concrete, +}; +use crate::physical_optimizer::PhysicalOptimizerRule; +use crate::physical_plan::rewrite::TreeNodeRewritable; +use crate::physical_plan::sorts::sort::SortExec; +use crate::physical_plan::windows::WindowAggExec; +use crate::physical_plan::{with_new_children_if_necessary, ExecutionPlan}; +use crate::prelude::SessionConfig; +use arrow::datatypes::SchemaRef; +use datafusion_common::{reverse_sort_options, DataFusionError}; +use datafusion_physical_expr::{PhysicalExpr, PhysicalSortExpr}; +use itertools::izip; +use std::iter::zip; +use std::sync::Arc; + +/// This rule inspects SortExec's in the given physical plan and removes the +/// ones it can prove unnecessary. +#[derive(Default)] +pub struct RemoveUnnecessarySorts {} + +impl RemoveUnnecessarySorts { + #[allow(missing_docs)] + pub fn new() -> Self { + Self {} + } +} + +/// This is a "data class" we use within the [RemoveUnnecessarySorts] rule +/// that tracks the closest `SortExec` descendant for every child of a plan. +#[derive(Debug, Clone)] +struct PlanWithCorrespondingSort { + plan: Arc<dyn ExecutionPlan>, + // For every child, keep a vector of `ExecutionPlan`s starting from the + // closest `SortExec` till the current plan. The first index of the tuple is + // the child index of the plan -- we need this information as we make updates. + sort_onwards: Vec<Vec<(usize, Arc<dyn ExecutionPlan>)>>, +} + +impl PlanWithCorrespondingSort { + pub fn new(plan: Arc<dyn ExecutionPlan>) -> Self { + let length = plan.children().len(); + PlanWithCorrespondingSort { + plan, + sort_onwards: vec![vec![]; length], + } + } + + pub fn children(&self) -> Vec<PlanWithCorrespondingSort> { + self.plan + .children() + .into_iter() + .map(|child| PlanWithCorrespondingSort::new(child)) + .collect() + } +} + +impl TreeNodeRewritable for PlanWithCorrespondingSort { + fn map_children<F>(self, transform: F) -> Result<Self> + where + F: FnMut(Self) -> Result<Self>, + { + let children = self.children(); + if children.is_empty() { + Ok(self) + } else { + let children_requirements = children + .into_iter() + .map(transform) + .collect::<Result<Vec<_>>>()?; + let children_plans = children_requirements + .iter() + .map(|elem| elem.plan.clone()) + .collect::<Vec<_>>(); + let sort_onwards = children_requirements + .iter() + .map(|item| { + if item.sort_onwards.is_empty() { + vec![] + } else { + // TODO: When `maintains_input_order` returns Vec<bool>, + // pass the order-enforcing sort upwards. + item.sort_onwards[0].clone() + } + }) + .collect::<Vec<_>>(); + let plan = with_new_children_if_necessary(self.plan, children_plans)?; + Ok(PlanWithCorrespondingSort { plan, sort_onwards }) + } + } +} + +impl PhysicalOptimizerRule for RemoveUnnecessarySorts { + fn optimize( + &self, + plan: Arc<dyn ExecutionPlan>, + _config: &SessionConfig, + ) -> Result<Arc<dyn ExecutionPlan>> { + // Execute a post-order traversal to adjust input key ordering: + let plan_requirements = PlanWithCorrespondingSort::new(plan); + let adjusted = plan_requirements.transform_up(&remove_unnecessary_sorts)?; + Ok(adjusted.plan) + } + + fn name(&self) -> &str { + "RemoveUnnecessarySorts" + } + + fn schema_check(&self) -> bool { + true + } +} + +fn remove_unnecessary_sorts( + requirements: PlanWithCorrespondingSort, +) -> Result<Option<PlanWithCorrespondingSort>> { + // Perform naive analysis at the beginning -- remove already-satisfied sorts: + if let Some(result) = analyze_immediate_sort_removal(&requirements)? { + return Ok(Some(result)); + } + let plan = &requirements.plan; + let mut new_children = plan.children().clone(); + let mut new_onwards = requirements.sort_onwards.clone(); + for (idx, (child, sort_onwards, required_ordering)) in izip!( + new_children.iter_mut(), + new_onwards.iter_mut(), + plan.required_input_ordering() + ) + .enumerate() + { + let physical_ordering = child.output_ordering(); + match (required_ordering, physical_ordering) { + (Some(required_ordering), Some(physical_ordering)) => { + let is_ordering_satisfied = ordering_satisfy_concrete( + physical_ordering, + required_ordering, + || child.equivalence_properties(), + ); + if !is_ordering_satisfied { + // Make sure we preserve the ordering requirements: + update_child_to_remove_unnecessary_sort(child, sort_onwards)?; + let sort_expr = required_ordering.to_vec(); + *child = add_sort_above_child(child, sort_expr)?; Review Comment: One thing we can do is to name the rule as `OptimizeSorts` instead of `RemoveUnnecessarySorts` so that others do not get thrown off by the sort adding code (which runs rarely, but needs to be there to cover corner cases @mustafasrepo explains). -- This is an automated message from the Apache Git Service. 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