TableInputFormatBase.java

  /**
   * Calculates the splits that will serve as input for the map tasks.
   * <ul>
   * Splits are created in number equal to the smallest between numSplits and
   * the number of {@link HRegion}s in the table. If the number of splits is
   * smaller than the number of {@link HRegion}s then splits are spanned across
   * multiple {@link HRegion}s and are grouped the most evenly possible. In the
   * case splits are uneven the bigger splits are placed first in the
   * {@link InputSplit} array.
   *
   * @param job the map task {@link JobConf}
   * @param numSplits a hint to calculate the number of splits (mapred.map.tasks).
   *
   * @return the input splits
   *
   * @see org.apache.hadoop.mapred.InputFormat#getSplits(org.apache.hadoop.mapred.JobConf, int)
   */
  public InputSplit[] getSplits(JobConf job, int numSplits) throws IOException {
    byte [][] startKeys = this.table.getStartKeys();
    if (startKeys == null || startKeys.length == 0) {
      throw new IOException("Expecting at least one region");
    }
    if (this.table == null) {
      throw new IOException("No table was provided");
    }
    if (this.inputColumns == null || this.inputColumns.length == 0) {
      throw new IOException("Expecting at least one column");
    }
    int realNumSplits = numSplits > startKeys.length? startKeys.length:
      numSplits;
    InputSplit[] splits = new InputSplit[realNumSplits];
    int middle = startKeys.length / realNumSplits;
    int startPos = 0;
    for (int i = 0; i < realNumSplits; i++) {
      int lastPos = startPos + middle;
      lastPos = startKeys.length % realNumSplits > i ? lastPos + 1 : lastPos;
      String regionLocation = table.getRegionLocation(startKeys[startPos]).
        getServerAddress().getHostname(); 
      splits[i] = new TableSplit(this.table.getTableName(),
        startKeys[startPos], ((i + 1) < realNumSplits) ? startKeys[lastPos]:
          HConstants.EMPTY_START_ROW, regionLocation);
      LOG.info("split: " + i + "->" + splits[i]);
      startPos = lastPos;
    }
    return splits;
  }