public static void setScannerCaching(JobConf job, int batchSize) {
    job.setInt("hbase.client.scanner.caching", batchSize);
  }
Sets the number of rows to return and cache with each scanner iteration. Higher caching values
will enable faster mapreduce jobs at the expense of requiring more heap to contain the cached
rows.
@param job       The current job configuration to adjust.
@param batchSize The number of rows to return in batch with each scanner iteration.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapred/TableMapReduceUtil.java