Lordworms commented on code in PR #9815: URL: https://github.com/apache/arrow-datafusion/pull/9815#discussion_r1542179422
########## datafusion/core/src/physical_optimizer/limit_pushdown.rs: ########## @@ -0,0 +1,127 @@ +// 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. + +//! The [`LimitPushdown`] The LimitPushdown optimization rule is designed +//! to improve the performance of query execution by pushing the LIMIT clause down +//! through the execution plan as far as possible, ideally directly +//! to the [`CoalesceBatchesExec`]. to reduce target_batch_size This means that instead of processing +//! a large amount of data and then applying the limit at the end, +//! the system tries to limit the amount of data being processed throughout the execution of the query. + +use std::sync::Arc; + +use crate::physical_optimizer::utils::is_global_limit; +use crate::physical_optimizer::PhysicalOptimizerRule; + +use crate::physical_plan::limit::GlobalLimitExec; +use crate::physical_plan::ExecutionPlan; +use datafusion_common::config::ConfigOptions; +use datafusion_common::tree_node::{Transformed, TransformedResult, TreeNode}; +use datafusion_common::Result; + +use datafusion_physical_plan::coalesce_batches::CoalesceBatchesExec; +use datafusion_physical_plan::coalesce_partitions::CoalescePartitionsExec; + +#[allow(missing_docs)] +pub struct LimitPushdown {} + +impl LimitPushdown { + #[allow(missing_docs)] + pub fn new() -> Self { + Self {} + } +} + +impl PhysicalOptimizerRule for LimitPushdown { + fn optimize( + &self, + plan: Arc<dyn ExecutionPlan>, + _config: &ConfigOptions, + ) -> Result<Arc<dyn ExecutionPlan>> { + // if this node is not a global limit, then directly return + if !is_global_limit(&plan) { + return Ok(plan); + } + // we traverse the treenode to try to push down the limit same logic as project push down + plan.transform_down(&push_down_limit).data() + } + + fn name(&self) -> &str { + "LimitPushdown" + } + + fn schema_check(&self) -> bool { + true + } +} +impl LimitPushdown {} +fn new_global_limit_with_input() {} +// try to push down current limit, based on the son +fn push_down_limit( + plan: Arc<dyn ExecutionPlan>, +) -> Result<Transformed<Arc<dyn ExecutionPlan>>> { + if let Some(global_limit) = plan.as_any().downcast_ref::<GlobalLimitExec>() { + let input = global_limit.input().as_any(); + if let Some(_) = input.downcast_ref::<CoalescePartitionsExec>() { + return Ok(Transformed::yes(swap_with_coalesce_partition(global_limit))); Review Comment: add more rules then. currently only specify to the repartition.slt test -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
