Github user rdblue commented on a diff in the pull request: https://github.com/apache/spark/pull/19424#discussion_r143591559 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/PushDownOperatorsToDataSource.scala --- @@ -0,0 +1,104 @@ +/* + * 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, Attribute, AttributeMap, Expression, PredicateHelper} +import org.apache.spark.sql.catalyst.optimizer.{PushDownPredicate, RemoveRedundantProject} +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. Operators are + * being pushed down with a specific order. As an example, given a LIMIT has a FILTER child, you + * can't push down LIMIT if FILTER is not completely pushed down. When both are pushed down, the + * data source should execute FILTER before LIMIT. And required columns are calculated at the end, + * because when more operators are pushed down, we may need less columns at Spark side. + */ +object PushDownOperatorsToDataSource extends Rule[LogicalPlan] with PredicateHelper { + override def apply(plan: LogicalPlan): LogicalPlan = { + // make sure filters are at very bottom. + val prepared = PushDownPredicate(plan) --- End diff -- Why apply this rule one more time? Is there reason to suspect that predicates won't already be pushed and that one more run would be worth it?
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