@Override
  public void start(long startKey, long endKey, int numThreads) throws IOException {
    super.start(startKey, endKey, numThreads);

    if (verbose) {
      LOG.debug("Inserting keys [" + startKey + ", " + endKey + ")");
    }

    createWriterThreads(numThreads);

    startThreads(writers);
  }
Use multi-puts vs. separate puts for every column in a row
hbase-diagnostics/src/main/java/org/apache/hadoop/hbase/util/MultiThreadedWriter.java