Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/13906#discussion_r69065025 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CollapseEmptyPlan.scala --- @@ -0,0 +1,49 @@ +/* + * 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. + */ + +package org.apache.spark.sql.catalyst.optimizer + +import org.apache.spark.sql.catalyst.expressions._ +import org.apache.spark.sql.catalyst.plans._ +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.catalyst.rules._ + +/** + * Collapse plans consisting empty local relations generated by [[PruneFilters]]. + * 1. InnerJoin with one or two empty children. + * 2. Project/Generate/Filter/Sample/Join/Limit/Union/Repartition with all empty children. + * 3. Aggregate with all empty children and grpExprs containing all aggExprs. + */ +object CollapseEmptyPlan extends Rule[LogicalPlan] with PredicateHelper { + private def isEmptyLocalRelation(plan: LogicalPlan): Boolean = + plan.isInstanceOf[LocalRelation] && plan.asInstanceOf[LocalRelation].data.isEmpty + + def apply(plan: LogicalPlan): LogicalPlan = plan transformUp { + case p @ Join(_, _, Inner, _) if p.children.exists(isEmptyLocalRelation) => --- End diff -- I think this rule is very useful, we can avoid scanning one join side if the other side is empty
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