| /* |
| * 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.wayang.core.optimizer.enumeration; |
| |
| import java.util.ArrayList; |
| import org.apache.wayang.core.api.Configuration; |
| |
| /** |
| * This {@link PlanEnumerationPruningStrategy} retains only the best {@code k} {@link PlanImplementation}s. |
| */ |
| public class TopKPruningStrategy implements PlanEnumerationPruningStrategy { |
| |
| private int k; |
| |
| @Override |
| public void configure(Configuration configuration) { |
| this.k = (int) configuration.getLongProperty("wayang.core.optimizer.pruning.topk", 5); |
| } |
| |
| @Override |
| public void prune(PlanEnumeration planEnumeration) { |
| // Skip if there is nothing to do... |
| if (planEnumeration.getPlanImplementations().size() <= this.k) return; |
| |
| ArrayList<PlanImplementation> planImplementations = new ArrayList<>(planEnumeration.getPlanImplementations()); |
| planImplementations.sort(this::comparePlanImplementations); |
| planEnumeration.getPlanImplementations().retainAll(planImplementations.subList(0, this.k)); |
| } |
| |
| |
| private int comparePlanImplementations(PlanImplementation p1, |
| PlanImplementation p2) { |
| final double t1 = p1.getSquashedCostEstimate(true); |
| final double t2 = p2.getSquashedCostEstimate(true); |
| return Double.compare(t1, t2); |
| } |
| |
| } |