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.asterix.optimizer.rules;
  
  import java.util.HashSet;
  import java.util.Set;
  
  import org.apache.asterix.om.functions.BuiltinFunctions;
  import org.apache.hyracks.algebricks.core.algebra.functions.FunctionIdentifier;
  import org.apache.hyracks.algebricks.rewriter.rules.PushFunctionsBelowJoin;
  
  /**
   * Pushes similarity function-call expressions below a join if possible.
   * Assigns the similarity function-call expressions to new variables, and replaces the original
   * expression with a corresponding variable reference expression.
   * This rule can help reduce the cost of computing expensive similarity functions by pushing them below
   * a join (which may blow up the cardinality).
   * Also, this rule may help to enable other rules such as common subexpression elimination, again to reduce
   * the number of calls to expensive similarity functions.
   * Example:
   * Before plan:
   * assign [$$10] <- [funcA(funcB(simFuncX($$3, $$4)))]
   * join (some condition)
   * join_branch_0 where $$3 and $$4 are not live
   * ...
   * join_branch_1 where $$3 and $$4 are live
   * ...
   * After plan:
   * assign [$$10] <- [funcA(funcB($$11))]
   * join (some condition)
   * join_branch_0 where $$3 and $$4 are not live
   * ...
   * join_branch_1 where $$3 and $$4 are live
   * assign[$$11] <- [simFuncX($$3, $$4)]
   * ...
   */
  public class PushSimilarityFunctionsBelowJoin extends PushFunctionsBelowJoin {
  
      private static final Set<FunctionIdentifier> simFuncIdents = new HashSet<FunctionIdentifier>();
      static {
          simFuncIdents.add(BuiltinFunctions.SIMILARITY_JACCARD);
          simFuncIdents.add(BuiltinFunctions.SIMILARITY_JACCARD_CHECK);
          simFuncIdents.add(BuiltinFunctions.EDIT_DISTANCE);
          simFuncIdents.add(BuiltinFunctions.EDIT_DISTANCE_CHECK);
      }
  
      public PushSimilarityFunctionsBelowJoin() {
          super(simFuncIdents);
      }
  }
  