avantgardnerio commented on code in PR #17347: URL: https://github.com/apache/datafusion/pull/17347#discussion_r2427604264
########## datafusion/physical-optimizer/src/limit_pushdown_past_window.rs: ########## @@ -0,0 +1,141 @@ +// 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 crate::PhysicalOptimizerRule; +use datafusion_common::config::ConfigOptions; +use datafusion_common::tree_node::{Transformed, TreeNode}; +use datafusion_common::ScalarValue; +use datafusion_expr::{WindowFrameBound, WindowFrameUnits}; +use datafusion_physical_plan::execution_plan::CardinalityEffect; +use datafusion_physical_plan::limit::GlobalLimitExec; +use datafusion_physical_plan::sorts::sort::SortExec; +use datafusion_physical_plan::windows::BoundedWindowAggExec; +use datafusion_physical_plan::ExecutionPlan; +use std::cmp; +use std::sync::Arc; + +/// This rule inspects [`ExecutionPlan`]'s attempting to find fetch limits that were not pushed +/// down by `LimitPushdown` because [BoundedWindowAggExec]s were "in the way". If the window is +/// bounded by [WindowFrameUnits::Rows] then we calculate the adjustment needed to grow the limit +/// and continue pushdown. +#[derive(Default, Clone, Debug)] +pub struct LimitPushPastWindows; + +impl LimitPushPastWindows { + pub fn new() -> Self { + Self + } +} + +impl PhysicalOptimizerRule for LimitPushPastWindows { + fn optimize( + &self, + original: Arc<dyn ExecutionPlan>, + config: &ConfigOptions, + ) -> datafusion_common::Result<Arc<dyn ExecutionPlan>> { + if !config.optimizer.enable_window_limits { + return Ok(original); + } + let mut latest_limit: Option<usize> = None; + let mut latest_max = 0; + let result = original.transform_down(|node| { + // helper closure to DRY out most the early return cases + let mut reset = |node, + max: &mut usize| + -> datafusion_common::Result< + Transformed<Arc<dyn ExecutionPlan>>, + > { + latest_limit = None; + *max = 0; + Ok(Transformed::no(node)) + }; + + // traversing sides of joins will require more thought + if node.children().len() > 1 { + return reset(node, &mut latest_max); + } + + // grab the latest limit we see + if let Some(limit) = node.as_any().downcast_ref::<GlobalLimitExec>() { + latest_limit = limit.fetch().map(|fetch| fetch + limit.skip()); + latest_max = 0; + return Ok(Transformed::no(node)); + } + + // grow the limit if we hit a window function + if let Some(window) = node.as_any().downcast_ref::<BoundedWindowAggExec>() { + for expr in window.window_expr().iter() { + let frame = expr.get_window_frame(); + if frame.units != WindowFrameUnits::Rows { Review Comment: I tried this and I think it's unsafe: ``` 1. query result mismatch: [SQL] SELECT SUM(c1) OVER (ORDER BY c2 DESC) as summation1 FROM null_cases LIMIT 5; [Diff] (-expected|+actual) - 962 - 962 - 962 - 962 - 962 + 263 + 263 + 263 + 263 + 263 ``` and ``` [Diff] (-expected|+actual) logical_plan 01)Projection: sum(null_cases.c1) ORDER BY [null_cases.c2 DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW AS summation1 02)--Limit: skip=0, fetch=5 03)----WindowAggr: windowExpr=[[sum(null_cases.c1) ORDER BY [null_cases.c2 DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW]] 04)------TableScan: null_cases projection=[c1, c2] physical_plan 01)ProjectionExec: expr=[sum(null_cases.c1) ORDER BY [null_cases.c2 DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW@2 as summation1] 02)--GlobalLimitExec: skip=0, fetch=5 03)----BoundedWindowAggExec: wdw=[sum(null_cases.c1) ORDER BY [null_cases.c2 DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW: Field { name: "sum(null_cases.c1) ORDER BY [null_cases.c2 DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW", data_type: Int64, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }, frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW], mode=[Sorted] - 04)------SortExec: expr=[c2@1 DESC], preserve_partitioning=[false] + 04)------SortExec: TopK(fetch=5), expr=[c2@1 DESC], preserve_partitioning=[false] 05)--------DataSourceExec: file_groups={1 group: [[WORKSPACE_ROOT/datafusion/core/tests/data/null_cases.csv]]}, projection=[c1, c2], file_type=csv, has_header=true ``` I think this is failing because there are multiple entries with the same value, so it needs more than the limit. -- This is an automated message from the Apache Git Service. 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