algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/InsertProjectBeforeUnionRule.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.hyracks.algebricks.rewriter.rules;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.lang3.mutable.Mutable;
import org.apache.commons.lang3.mutable.MutableObject;

import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
import org.apache.hyracks.algebricks.common.utils.Triple;
import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
import org.apache.hyracks.algebricks.core.algebra.base.IOptimizationContext;
import org.apache.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
import org.apache.hyracks.algebricks.core.algebra.base.LogicalVariable;
import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
import org.apache.hyracks.algebricks.core.algebra.operators.logical.ProjectOperator;
import org.apache.hyracks.algebricks.core.algebra.operators.logical.UnionAllOperator;
import org.apache.hyracks.algebricks.core.algebra.operators.logical.visitors.VariableUtilities;
import org.apache.hyracks.algebricks.core.algebra.operators.physical.StreamProjectPOperator;
import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;

public class InsertProjectBeforeUnionRule implements IAlgebraicRewriteRule {

    @Override
    public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
            throws AlgebricksException {
        return false;
    }

    /**
     * When the input schema to WriteOperator is different from the output
     * schema in terms of variable order, add a project operator to get the
     * write order
     */
    @Override
    public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context) throws AlgebricksException {
        AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
        if (op.getOperatorTag() != LogicalOperatorTag.UNIONALL) {
            return false;
        }
        UnionAllOperator opUnion = (UnionAllOperator) op;
        List<Triple<LogicalVariable, LogicalVariable, LogicalVariable>> varMap = opUnion.getVariableMappings();
        ArrayList<LogicalVariable> usedVariablesFromOne = new ArrayList<LogicalVariable>();
        ArrayList<LogicalVariable> usedVariablesFromTwo = new ArrayList<LogicalVariable>();

        for (Triple<LogicalVariable, LogicalVariable, LogicalVariable> triple : varMap) {
            usedVariablesFromOne.add(triple.first);
            usedVariablesFromTwo.add(triple.second);
        }

        ArrayList<LogicalVariable> inputSchemaOne = new ArrayList<LogicalVariable>();
        VariableUtilities.getLiveVariables(opUnion.getInputs().get(0).getValue(), inputSchemaOne);

        ArrayList<LogicalVariable> inputSchemaTwo = new ArrayList<LogicalVariable>();
        VariableUtilities.getLiveVariables(opUnion.getInputs().get(1).getValue(), inputSchemaTwo);

        boolean rewritten = false;
        if (!isIdentical(usedVariablesFromOne, inputSchemaOne)) {
            insertProjectOperator(opUnion, 0, usedVariablesFromOne, context);
            rewritten = true;
        }
        if (!isIdentical(usedVariablesFromTwo, inputSchemaTwo)) {
            insertProjectOperator(opUnion, 1, usedVariablesFromTwo, context);
            rewritten = true;
        }
        return rewritten;
    }

    private void insertProjectOperator(UnionAllOperator opUnion, int branch, ArrayList<LogicalVariable> usedVariables,
            IOptimizationContext context) throws AlgebricksException {
        ProjectOperator projectOp = new ProjectOperator(usedVariables);
        ILogicalOperator parentOp = opUnion.getInputs().get(branch).getValue();
        projectOp.getInputs().add(new MutableObject<ILogicalOperator>(parentOp));
        opUnion.getInputs().get(branch).setValue(projectOp);
        projectOp.setPhysicalOperator(new StreamProjectPOperator());
        context.computeAndSetTypeEnvironmentForOperator(projectOp);
        context.computeAndSetTypeEnvironmentForOperator(parentOp);
    }

    private boolean isIdentical(List<LogicalVariable> finalSchema, List<LogicalVariable> inputSchema)
            throws AlgebricksException {
        int finalSchemaSize = finalSchema.size();
        int inputSchemaSize = inputSchema.size();
        if (finalSchemaSize != inputSchemaSize) {
            return false;
        }
        for (int i = 0; i < finalSchemaSize; i++) {
            LogicalVariable var1 = finalSchema.get(i);
            LogicalVariable var2 = inputSchema.get(i);
            if (!var1.equals(var2))
                return false;
        }
        return true;
    }

}