@Override
  public HFileScanner getScanner(Configuration conf, boolean cacheBlocks, final boolean pread) {
    return getScanner(conf, cacheBlocks, pread, false);
  }
Create a Scanner on this file. No seeks or reads are done on creation. Call
{@link HFileScanner#seekTo(ExtendedCell)} to position an start the read. There is nothing to
clean up in a Scanner. Letting go of your references to the scanner is sufficient. NOTE: Do not
use this overload of getScanner for compactions. See
{@link #getScanner(Configuration, boolean, boolean, boolean)}
@param conf        Store configuration.
@param cacheBlocks True if we should cache blocks read in by this scanner.
@param pread       Use positional read rather than seek+read if true (pread is better for
                   random reads, seek+read is better scanning).
@return Scanner on this file.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java