flink-optimizer/src/main/java/org/apache/flink/optimizer/traversals/InterestingPropertyVisitor.java

/*
 * 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.flink.optimizer.traversals;

import org.apache.flink.optimizer.costs.CostEstimator;
import org.apache.flink.optimizer.dag.OptimizerNode;
import org.apache.flink.util.Visitor;

/**
 * Visitor that computes the interesting properties for each node in the optimizer DAG. On its
 * recursive depth-first descend, it propagates all interesting properties top-down.
 */
public class InterestingPropertyVisitor implements Visitor<OptimizerNode> {

    private CostEstimator
            estimator; // the cost estimator for maximal costs of an interesting property

    /**
     * Creates a new visitor that computes the interesting properties for all nodes in the plan. It
     * uses the given cost estimator used to compute the maximal costs for an interesting property.
     *
     * @param estimator The cost estimator to estimate the maximal costs for interesting properties.
     */
    public InterestingPropertyVisitor(CostEstimator estimator) {
        this.estimator = estimator;
    }

    @Override
    public boolean preVisit(OptimizerNode node) {
        // The interesting properties must be computed on the descend. In case a node has multiple
        // outputs,
        // that computation must happen during the last descend.

        if (node.getInterestingProperties() == null
                && node.haveAllOutputConnectionInterestingProperties()) {
            node.computeUnionOfInterestingPropertiesFromSuccessors();
            node.computeInterestingPropertiesForInputs(this.estimator);
            return true;
        } else {
            return false;
        }
    }

    @Override
    public void postVisit(OptimizerNode visitable) {}
}