[GitHub] [arrow] Dandandan commented on a change in pull request #8961: ARROW-10885: [Rust][DataFusion] Optimize hash join build vs probe order based on number of rows

[GitBox <gi...@apache.org>]

Dandandan commented on a change in pull request #8961:
URL: https://github.com/apache/arrow/pull/8961#discussion_r545873082



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File path: rust/datafusion/src/optimizer/hash_build_probe_order.rs
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@@ -0,0 +1,218 @@
+// 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
+
+//! Optimizer rule to switch build and probe order of hash join
+//! based on statistics of a `TableProvider`. If the number of
+//! rows of both sources is known, the order can be switched
+//! for a faster hash join.
+
+use crate::logical_plan::LogicalPlan;
+use crate::optimizer::optimizer::OptimizerRule;
+use crate::{error::Result, prelude::JoinType};
+
+use super::utils;
+
+/// BuildProbeOrder reorders the build and probe phase of
+/// hash joins. This uses the amount of rows that a datasource has.
+/// The rule optimizes the order such that the left (build) side of the join
+/// is the smallest.
+/// If the information is not available, the order stays the same,
+/// so that it could be optimized manually in a query.
+pub struct HashBuildProbeOrder {}
+
+// Gets exact number of rows, if known by the statistics of the underlying
+fn get_num_rows(logical_plan: &LogicalPlan) -> Option<usize> {
+    match logical_plan {
+        LogicalPlan::Projection { input, .. } => get_num_rows(input),
+        LogicalPlan::Sort { input, .. } => get_num_rows(input),
+        LogicalPlan::TableScan { source, .. } => source.statistics().num_rows,
+        LogicalPlan::EmptyRelation {

Review comment:
       Not sure if this is relevant, where this is used?




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