content: /*
   * 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.calcite.rel.rules;
  
  import org.apache.calcite.plan.RelOptRuleCall;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Intersect;
  import org.apache.calcite.rel.logical.LogicalIntersect;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.tools.RelBuilder;
  
  import org.immutables.value.Value;
  
  import java.util.Comparator;
  import java.util.List;
  import java.util.stream.Collectors;
  
  /**
   * Planner rule that reorders inputs of an {@link Intersect} to put smaller inputs first.
   * This helps reduce the size of intermediate results.
   *
   * <p>Intersect(A, B, ...) where B is smallest will reorder to Intersect(B, A, ...)
   */
  @Value.Enclosing
  public class IntersectReorderRule extends RelRule<IntersectReorderRule.Config>
        implements SubstitutionRule {
    /** Creates an IntersectReorderRule. */
    protected IntersectReorderRule(Config config) {
      super(config);
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final Intersect intersect = call.rel(0);
      final RelMetadataQuery mq = call.getMetadataQuery();
      final List<RelNode> inputs = intersect.getInputs();
  
      List<RelNode> sortedInputs = inputs.stream()
          .sorted(Comparator.comparingDouble(mq::getRowCount))
          .collect(Collectors.toList());
  
      if (inputs.equals(sortedInputs)) {
        return;
      }
  
      final RelBuilder relBuilder = call.builder();
      relBuilder.pushAll(sortedInputs);
      relBuilder.intersect(intersect.all, sortedInputs.size());
  
      call.transformTo(relBuilder.build());
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableIntersectReorderRule.Config.of()
          .withOperandSupplier(b0 ->
              b0.operand(LogicalIntersect.class)
                  .predicate(intersect -> intersect.getInputs().size() > 1)
                  .anyInputs())
          .withDescription("IntersectReorderRule");
  
      @Override default IntersectReorderRule toRule() {
        return new IntersectReorderRule(this);
      }
    }
  }
  