sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/planner/RelMdNodeStats.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.beam.sdk.extensions.sql.impl.planner;

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import org.apache.beam.sdk.extensions.sql.impl.rel.BeamRelNode;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.RelNode;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.metadata.MetadataDef;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.metadata.MetadataHandler;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.metadata.ReflectiveRelMetadataProvider;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.metadata.RelMetadataProvider;
import org.apache.beam.vendor.calcite.v1_20_0.org.apache.calcite.rel.metadata.RelMetadataQuery;

/**
 * This is the implementation of NodeStatsMetadata. Methods to estimate rate and row count for
 * Calcite's logical nodes be implemented here.
 */
public class RelMdNodeStats implements MetadataHandler<NodeStatsMetadata> {

  public static final RelMetadataProvider SOURCE =
      ReflectiveRelMetadataProvider.reflectiveSource(
          NodeStatsMetadata.METHOD, new RelMdNodeStats());

  @Override
  public MetadataDef<NodeStatsMetadata> getDef() {
    return NodeStatsMetadata.DEF;
  }

  @SuppressWarnings("UnusedDeclaration")
  public NodeStats getNodeStats(RelNode rel, RelMetadataQuery mq) {

    if (rel instanceof BeamRelNode) {
      return this.getBeamNodeStats((BeamRelNode) rel, mq);
    }

    // We can later define custom methods for all different RelNodes to prevent hitting this point.
    // Similar to RelMdRowCount in calcite.

    return NodeStats.UNKNOWN;
  }

  private NodeStats getBeamNodeStats(BeamRelNode rel, RelMetadataQuery mq) {

    // Removing the unknown results.
    // Calcite caches previous results in mq.map. This is done to prevent cyclic calls of this
    // method and also improving the performance. However, we might have returned an unknown result
    // because one of the inputs of the node was unknown (it is a logical node that we have not
    // implemented getNodeStats for it). Later we should not get the Unknown, therefore we need to
    // remove unknown results everyTime that this method is called.
    // Results are also cached in CachingRelMetadataProvider because calcite PlannerImpl#Transform
    // wraps the metadata provider with CachingRelMetadataProvider. However,
    // CachingRelMetadataProvider checks timestamp before returning previous results. Therefore,
    // there wouldn't be a problem in that case.
    List<List> keys =
        mq.map.entrySet().stream()
            .filter(entry -> entry.getValue() instanceof NodeStats)
            .filter(entry -> ((NodeStats) entry.getValue()).isUnknown())
            .map(Map.Entry::getKey)
            .collect(Collectors.toList());

    for (List key : keys) {
      mq.map.remove(key);
    }

    return rel.estimateNodeStats(mq);
  }
}