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.beam.sdk.extensions.sql.impl.planner;
  
  import java.lang.reflect.Method;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.linq4j.tree.Types;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.RelNode;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.metadata.Metadata;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.metadata.MetadataDef;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.metadata.MetadataHandler;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.metadata.RelMetadataQuery;
  
  /**
   * This is a metadata used for row count and rate estimation. It extends Calcite's Metadata
   * interface so that we can use MetadataQuery to get our own estimates.
   */
  public interface NodeStatsMetadata extends Metadata {
    Method METHOD = Types.lookupMethod(NodeStatsMetadata.class, "getNodeStats");
  
    MetadataDef<NodeStatsMetadata> DEF =
        MetadataDef.of(NodeStatsMetadata.class, NodeStatsMetadata.Handler.class, METHOD);
  
    // In order to use this we need to call it by relNode.metadata(NodeStatsMetadata.class,
    // mq).getNodeStats() where mq is the MetadataQuery (can be obtained by
    // relNode.getCluster().getMetadataQuery()). After this, Calcite looks for the implementation of
    // this metadata that we have registered in MetadataProvider (it is RelMdNodeStats.class in
    // this case and we have registered it in CalciteQueryPlanner). Then Calcite's generated Code
    // decides the type of the rel node and calls appropriate method in RelMdNodeStats.
    // For instance: Join is a subclass of RelNode and if we have both getNodeStats(RelNode rel,
    // RelMetadataQuery mq) and getNodeStats(Join rel, RelMetadataQuery mq) then if the rel is an
    // instance of Join it will call getNodeStats((Join) rel, mq).
    // Currently we only register it in SQLTransform path. JDBC does not register this and it does not
    // use it. (because it does not register the our NonCumulativeMetadata implementation either).
    NodeStats getNodeStats();
  
    /** Handler API. */
    interface Handler extends MetadataHandler<NodeStatsMetadata> {
      NodeStats getNodeStats(RelNode r, RelMetadataQuery mq);
    }
  }
  