Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/19424#discussion_r142806719 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/PushDownOperatorsToDataSource.scala --- @@ -0,0 +1,99 @@ +/* + * 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.execution.datasources.v2 + +import org.apache.spark.sql.catalyst.expressions.{And, AttributeMap, AttributeSet, Expression, ExpressionSet} +import org.apache.spark.sql.catalyst.planning.PhysicalOperation +import org.apache.spark.sql.catalyst.plans.logical.{Filter, LogicalPlan, Project} +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.execution.datasources.DataSourceStrategy +import org.apache.spark.sql.sources +import org.apache.spark.sql.sources.v2.reader._ + +/** + * Pushes down various operators to the underlying data source for better performance. We classify + * operators into different layers, operators in the same layer are orderless, i.e. the query result + * won't change if we switch the operators within a layer(e.g. we can switch the order of predicates + * and required columns). The operators in layer N can only be pushed down if operators in layer N-1 + * that above the data source relation are all pushed down. As an example, you can't push down limit + * if a filter below limit is not pushed down. + * + * Current operator push down layers: + * layer 1: predicates, required columns. + */ +object PushDownOperatorsToDataSource extends Rule[LogicalPlan] { + override def apply(plan: LogicalPlan): LogicalPlan = { --- End diff -- This is an optimizer rule? The input is a `LogicalPlan` and the output is still a `LogicalPlan`?
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