org.trend.hgraph.mapreduce.pagerank.CalculatePageRankReducer.java Source code

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Here is the source code for org.trend.hgraph.mapreduce.pagerank.CalculatePageRankReducer.java

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/**
 * 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.trend.hgraph.mapreduce.pagerank;

import java.io.IOException;
import java.math.BigDecimal;
import java.math.RoundingMode;

import org.apache.commons.lang.time.StopWatch;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import org.trend.hgraph.HBaseGraphConstants;

/**
 * A <code>Reducer</code> for calculating new pageranks by its upstream <code>Mapper</code>s.
 * @author scott_miao
 * @see CalculateInitPageRankMapper
 * @see CalculateIntermediatePageRankMapper
 */
public class CalculatePageRankReducer extends Reducer<Text, DoubleWritable, Text, DoubleWritable> {

    public static enum Counters {
        CHANGED_PAGE_RANK_COUNT, CAL_NEW_PR_TIME_CONSUMED, CMP_OLD_NEW_PR_TIME_CONSUMED
    }

    private double verticesTotalCnt = 1.0D;
    private double dampingFactor = Constants.PAGE_RANK_DAMPING_FACTOR_DEFAULT_VALUE;
    private HTable vertexTable = null;
    private int pageRankCompareScale = 3;

    /*
     * (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.Reducer#reduce(java.lang.Object, java.lang.Iterable, Context)
     */
    @Override
    protected void reduce(Text key, Iterable<DoubleWritable> incomingPageRanks, Context context)
            throws IOException, InterruptedException {

        String rowkey = Bytes.toString(key.getBytes()).trim();
        double incomingPageRankSum = 0.0D;
        StopWatch sw = new StopWatch();
        sw.start();
        for (DoubleWritable incomingPageRank : incomingPageRanks) {
            incomingPageRankSum = incomingPageRankSum + incomingPageRank.get();
        }
        // calculate new pageRank here
        double newPageRank = (dampingFactor * incomingPageRankSum) + ((1.0D - dampingFactor) / verticesTotalCnt);
        sw.stop();
        context.getCounter(Counters.CAL_NEW_PR_TIME_CONSUMED).increment(sw.getTime());

        sw.reset();
        sw.start();
        double oldPageRank = Utils.getPageRank(vertexTable, rowkey, Constants.PAGE_RANK_CQ_TMP_NAME);
        if (!pageRankEquals(oldPageRank, newPageRank, pageRankCompareScale)) {
            // collect pageRank changing count with counter
            context.getCounter(Counters.CHANGED_PAGE_RANK_COUNT).increment(1);
        }
        sw.stop();
        context.getCounter(Counters.CMP_OLD_NEW_PR_TIME_CONSUMED).increment(sw.getTime());

        context.write(key, new DoubleWritable(newPageRank));
    }

    static boolean pageRankEquals(double src, double dest, int scale) {
        BigDecimal a = new BigDecimal(src);
        BigDecimal b = new BigDecimal(dest);
        a = a.setScale(scale, RoundingMode.DOWN);
        b = b.setScale(scale, RoundingMode.DOWN);
        return a.compareTo(b) == 0 ? true : false;
    }

    /*
     * (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.Reducer#setup(org.apache.hadoop.mapreduce.Reducer.Context)
     */
    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
        Configuration conf = context.getConfiguration();

        vertexTable = Utils.initTable(conf, HBaseGraphConstants.HBASE_GRAPH_TABLE_VERTEX_NAME_KEY, this.getClass());

        String value = conf.get(Constants.PAGE_RANK_VERTICES_TOTAL_COUNT_KEY);
        if (null != value)
            verticesTotalCnt = Double.parseDouble(value);

        value = conf.get(Constants.PAGE_RANK_DAMPING_FACTOR_KEY);
        if (null != value)
            dampingFactor = Double.parseDouble(value);
    }

    /*
     * (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.Reducer#cleanup(org.apache.hadoop.mapreduce.Reducer.Context)
     */
    @Override
    protected void cleanup(Context context) throws IOException, InterruptedException {
        vertexTable.close();
    }

}