tajo-core/src/main/java/org/apache/tajo/engine/planner/physical/HashLeftOuterJoinExec.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.tajo.engine.planner.physical;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.tajo.plan.logical.JoinNode;
import org.apache.tajo.storage.Tuple;
import org.apache.tajo.worker.TaskAttemptContext;

import java.io.IOException;
import java.util.Iterator;
import java.util.List;

public class HashLeftOuterJoinExec extends HashJoinExec {

  private static final Log LOG = LogFactory.getLog(HashLeftOuterJoinExec.class);
  private final List<Tuple> nullTupleList;

  public HashLeftOuterJoinExec(TaskAttemptContext context, JoinNode plan, PhysicalExec leftChild,
                               PhysicalExec rightChild) {
    super(context, plan, leftChild, rightChild);
    nullTupleList = nullTupleList(rightNumCols);
  }

  @Override
  public Tuple next() throws IOException {
    if (first) {
      loadRightToHashTable();
    }

    while (!context.isStopped() && !finished) {
      if (iterator != null && iterator.hasNext()) {
        frameTuple.setRight(iterator.next());
        return projector.eval(frameTuple);
      }
      Tuple leftTuple = leftChild.next(); // it comes from a disk
      if (leftTuple == null) { // if no more tuples in left tuples on disk, a join is completed.
        finished = true;
        return null;
      }
      frameTuple.setLeft(leftTuple);

      if (leftFiltered(leftTuple)) {
        iterator = nullTupleList.iterator();
        continue;
      }

      // getting corresponding right
      TupleList hashed = tupleSlots.get(leftKeyExtractor.project(leftTuple));
      Iterator<Tuple> rightTuples = rightFiltered(hashed);
      if (!rightTuples.hasNext()) {
        //this left tuple doesn't have a match on the right.But full outer join => we should keep it anyway
        //output a tuple with the nulls padded rightTuple
        iterator = nullTupleList.iterator();
        continue;
      }
      iterator = rightTuples;
    }

    return null;
  }
}