asterixdb/asterix-algebra/src/main/java/org/apache/asterix/optimizer/rules/PushSimilarityFunctionsBelowJoin.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.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);
    }
}