com.yahoo.rdfpig.optimizer.OnceDynamicOptimizationStrategy.java Source code

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Here is the source code for com.yahoo.rdfpig.optimizer.OnceDynamicOptimizationStrategy.java

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/*
 * Copyright 2011 Yahoo! Inc.
 *
 * Licensed 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 com.yahoo.rdfpig.optimizer;

import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;

import org.apache.commons.math.stat.descriptive.moment.StandardDeviation;
import org.openrdf.query.algebra.TupleExpr;

import com.yahoo.rdfpig.costcalculators.SamplingCardinalityCalculator;
import com.yahoo.rdfpig.optimizer.EfficientJoinOptimizer.SearchPath;

/**
 * Simple dynamic optimization strategy that just evaluates the NUMBEROFPLANSPERBATCH cheapest sub-plans.
 * @author spyros
 *
 */
public class OnceDynamicOptimizationStrategy implements DynamicOptimizationStrategy {

    boolean firstTime = true;
    private StandardDeviation stdDev = new StandardDeviation();

    /* (non-Javadoc)
     * @see eu.larkc.RDFPig.optimizers.DynamicOptimizationStrategy#checkDynamicOptimizationDone(org.openrdf.query.algebra.TupleExpr)
     */
    @Override
    public boolean checkDynamicOptimizationDone(TreeSet<SearchPath> candidates) {
        if (firstTime) {
            firstTime = false;
            return false;
        } else
            return true;

    }

    /* (non-Javadoc)
     * @see eu.larkc.RDFPig.optimizers.DynamicOptimizationStrategy#selectPlans(java.util.TreeSet, eu.larkc.RDFPig.costCalculators.AbstractCostCalculator)
     */
    @Override
    public Set<TupleExpr> selectPlans(TreeSet<SearchPath> candidates, SamplingCardinalityCalculator calculator) {
        HashSet<TupleExpr> ret = new HashSet<TupleExpr>();

        double[] costs = new double[candidates.size()];
        int i = 0;
        for (SearchPath p : candidates)
            costs[i++] = p.cost;

        double dev = stdDev.evaluate(costs);

        int plansPerSubgraph = (int) dev + 1;

        i = 0;
        for (SearchPath p : candidates) {
            if (!calculator.isCalculated(p.current) && !calculator.isSampled(p.current)) {
                ret.add(p.current);

                if (i++ > plansPerSubgraph)
                    break;
            }
        }
        return ret;
    }
}