001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce.lib.db;
020
021import java.math.BigDecimal;
022import java.sql.ResultSet;
023import java.sql.SQLException;
024import java.util.ArrayList;
025import java.util.List;
026
027import org.apache.commons.logging.Log;
028import org.apache.commons.logging.LogFactory;
029
030import org.apache.hadoop.classification.InterfaceAudience;
031import org.apache.hadoop.classification.InterfaceStability;
032import org.apache.hadoop.conf.Configuration;
033import org.apache.hadoop.mapreduce.InputSplit;
034import org.apache.hadoop.mapreduce.MRJobConfig;
035
036/**
037 * Implement DBSplitter over BigDecimal values.
038 */
039@InterfaceAudience.Public
040@InterfaceStability.Evolving
041public class BigDecimalSplitter implements DBSplitter {
042  private static final Log LOG = LogFactory.getLog(BigDecimalSplitter.class);
043
044  public List<InputSplit> split(Configuration conf, ResultSet results, String colName)
045      throws SQLException {
046
047    BigDecimal minVal = results.getBigDecimal(1);
048    BigDecimal maxVal = results.getBigDecimal(2);
049
050    String lowClausePrefix = colName + " >= ";
051    String highClausePrefix = colName + " < ";
052
053    BigDecimal numSplits = new BigDecimal(conf.getInt(MRJobConfig.NUM_MAPS, 1));
054
055    if (minVal == null && maxVal == null) {
056      // Range is null to null. Return a null split accordingly.
057      List<InputSplit> splits = new ArrayList<InputSplit>();
058      splits.add(new DataDrivenDBInputFormat.DataDrivenDBInputSplit(
059          colName + " IS NULL", colName + " IS NULL"));
060      return splits;
061    }
062
063    if (minVal == null || maxVal == null) {
064      // Don't know what is a reasonable min/max value for interpolation. Fail.
065      LOG.error("Cannot find a range for NUMERIC or DECIMAL fields with one end NULL.");
066      return null;
067    }
068
069    // Get all the split points together.
070    List<BigDecimal> splitPoints = split(numSplits, minVal, maxVal);
071    List<InputSplit> splits = new ArrayList<InputSplit>();
072
073    // Turn the split points into a set of intervals.
074    BigDecimal start = splitPoints.get(0);
075    for (int i = 1; i < splitPoints.size(); i++) {
076      BigDecimal end = splitPoints.get(i);
077
078      if (i == splitPoints.size() - 1) {
079        // This is the last one; use a closed interval.
080        splits.add(new DataDrivenDBInputFormat.DataDrivenDBInputSplit(
081            lowClausePrefix + start.toString(),
082            colName + " <= " + end.toString()));
083      } else {
084        // Normal open-interval case.
085        splits.add(new DataDrivenDBInputFormat.DataDrivenDBInputSplit(
086            lowClausePrefix + start.toString(),
087            highClausePrefix + end.toString()));
088      }
089
090      start = end;
091    }
092
093    return splits;
094  }
095
096  private static final BigDecimal MIN_INCREMENT = new BigDecimal(10000 * Double.MIN_VALUE);
097
098  /**
099   * Divide numerator by denominator. If impossible in exact mode, use rounding.
100   */
101  protected BigDecimal tryDivide(BigDecimal numerator, BigDecimal denominator) {
102    try {
103      return numerator.divide(denominator);
104    } catch (ArithmeticException ae) {
105      return numerator.divide(denominator, BigDecimal.ROUND_HALF_UP);
106    }
107  }
108
109  /**
110   * Returns a list of BigDecimals one element longer than the list of input splits.
111   * This represents the boundaries between input splits.
112   * All splits are open on the top end, except the last one.
113   *
114   * So the list [0, 5, 8, 12, 18] would represent splits capturing the intervals:
115   *
116   * [0, 5)
117   * [5, 8)
118   * [8, 12)
119   * [12, 18] note the closed interval for the last split.
120   */
121  List<BigDecimal> split(BigDecimal numSplits, BigDecimal minVal, BigDecimal maxVal)
122      throws SQLException {
123
124    List<BigDecimal> splits = new ArrayList<BigDecimal>();
125
126    // Use numSplits as a hint. May need an extra task if the size doesn't
127    // divide cleanly.
128
129    BigDecimal splitSize = tryDivide(maxVal.subtract(minVal), (numSplits));
130    if (splitSize.compareTo(MIN_INCREMENT) < 0) {
131      splitSize = MIN_INCREMENT;
132      LOG.warn("Set BigDecimal splitSize to MIN_INCREMENT");
133    }
134
135    BigDecimal curVal = minVal;
136
137    while (curVal.compareTo(maxVal) <= 0) {
138      splits.add(curVal);
139      curVal = curVal.add(splitSize);
140    }
141
142    if (splits.get(splits.size() - 1).compareTo(maxVal) != 0 || splits.size() == 1) {
143      // We didn't end on the maxVal. Add that to the end of the list.
144      splits.add(maxVal);
145    }
146
147    return splits;
148  }
149}