fe/src/main/java/org/apache/impala/planner/EmptySetNode.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.impala.planner;

import java.util.List;

import org.apache.impala.analysis.Analyzer;
import org.apache.impala.analysis.TupleId;
import org.apache.impala.thrift.TExplainLevel;
import org.apache.impala.thrift.TPlanNode;
import org.apache.impala.thrift.TPlanNodeType;
import org.apache.impala.thrift.TQueryOptions;

import com.google.common.base.Preconditions;

/**
 * Node that returns an empty result set. Used for planning query blocks with a constant
 * predicate evaluating to false or a limit 0. The result set will have zero rows, but
 * the row descriptor must still include a materialized tuple so that the backend can
 * construct a valid row empty batch.
 */
public class EmptySetNode extends PlanNode {
  public EmptySetNode(PlanNodeId id, List<TupleId> tupleIds) {
    super(id, tupleIds, "EMPTYSET");
    Preconditions.checkArgument(tupleIds.size() > 0);
  }

  @Override
  public void computeStats(Analyzer analyzer) {
    avgRowSize_ = 0;
    cardinality_ = 0;
    numNodes_ = 1;
  }

  @Override
  public void init(Analyzer analyzer) {
    Preconditions.checkState(conjuncts_.isEmpty());
    // If the physical output tuple produced by an AnalyticEvalNode wasn't created
    // the logical output tuple is returned by getMaterializedTupleIds(). It needs
    // to be set as materialized (even though it isn't) to avoid failing precondition
    // checks generating the thrift for slot refs that may reference this tuple.
    for (TupleId id: tupleIds_) analyzer.getTupleDesc(id).setIsMaterialized(true);
    computeMemLayout(analyzer);
    computeStats(analyzer);
  }

  @Override
  public void computeNodeResourceProfile(TQueryOptions queryOptions) {
    // TODO: add an estimate
    nodeResourceProfile_ = ResourceProfile.noReservation(0);
  }

  @Override
  protected String getNodeExplainString(String prefix, String detailPrefix,
      TExplainLevel detailLevel) {
    return String.format("%s%s:%s\n", prefix, id_.toString(), displayName_);
  }

  @Override
  protected void toThrift(TPlanNode msg) {
    msg.node_type = TPlanNodeType.EMPTY_SET_NODE;
  }

  @Override
  protected boolean displayCardinality(TExplainLevel detailLevel) { return false; }
}