Push the limits past window functions #17347
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| // 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. | ||
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| 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; | ||
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| /// 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; | ||
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| impl LimitPushPastWindows { | ||
| pub fn new() -> Self { | ||
| Self | ||
| } | ||
| } | ||
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| 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)) | ||
| }; | ||
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| // traversing sides of joins will require more thought | ||
| if node.children().len() > 1 { | ||
| return reset(node, &mut latest_max); | ||
| } | ||
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| // 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)); | ||
| } | ||
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| // 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 { | ||
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Contributor
There was a problem hiding this comment. As far as I can see, we update SELECT
c9,
SUM(c9) OVER(ORDER BY c9 ASC RANGE BETWEEN 5 PRECEDING AND 1 PRECEDING) as sum1
FROM aggregate_test_100
LIMIT 5However, we can do this change in subsequent PRs. I think in current form, this PR is correct and we can merge as is. Thanks @avantgardnerio for this PR.
Contributor
Author
There was a problem hiding this comment. Good point! I will file a subsequent PR 😄
Contributor
Author
There was a problem hiding this comment. I tried this and I think it's unsafe: and I think this is failing because there are multiple entries with the same value, so it needs more than the limit.
Contributor
There was a problem hiding this comment. However, for this case end bound is |
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| return reset(node, &mut latest_max); // expression-based limits? | ||
| } | ||
| let Some(end_bound) = bound_to_usize(&frame.end_bound) else { | ||
| return reset(node, &mut latest_max); | ||
| }; | ||
| latest_max = cmp::max(end_bound, latest_max); | ||
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| } | ||
| return Ok(Transformed::no(node)); | ||
| } | ||
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| // Apply the limit if we hit a sort node | ||
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| if let Some(sort) = node.as_any().downcast_ref::<SortExec>() { | ||
| let latest = latest_limit.take(); | ||
| let Some(fetch) = latest else { | ||
| latest_max = 0; | ||
| return Ok(Transformed::no(node)); | ||
| }; | ||
| let fetch = match sort.fetch() { | ||
| None => fetch + latest_max, | ||
| Some(existing) => cmp::min(existing, fetch + latest_max), | ||
| }; | ||
| let sort: Arc<dyn ExecutionPlan> = Arc::new(sort.with_fetch(Some(fetch))); | ||
| latest_max = 0; | ||
| return Ok(Transformed::complete(sort)); | ||
| } | ||
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| // we can't push the limit past nodes that decrease row count | ||
| match node.cardinality_effect() { | ||
| CardinalityEffect::Equal => {} | ||
| _ => return reset(node, &mut latest_max), | ||
| } | ||
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| Ok(Transformed::no(node)) | ||
| })?; | ||
| Ok(result.data) | ||
| } | ||
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| fn name(&self) -> &str { | ||
| "LimitPushPastWindows" | ||
| } | ||
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| fn schema_check(&self) -> bool { | ||
| false // we don't change the schema | ||
| } | ||
| } | ||
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| fn bound_to_usize(bound: &WindowFrameBound) -> Option<usize> { | ||
| match bound { | ||
| WindowFrameBound::Preceding(_) => Some(0), | ||
| WindowFrameBound::CurrentRow => Some(0), | ||
| WindowFrameBound::Following(ScalarValue::UInt64(Some(scalar))) => { | ||
| Some(*scalar as usize) | ||
| } | ||
| _ => None, | ||
| } | ||
| } | ||
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| // tests: all branches are covered by sqllogictests | ||
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