public int read(long position, byte[] buffer, int offset, int length) throws IOException {
    if (!(rawStream instanceof PositionedReadable)) {
      throw new UnsupportedOperationException(
        "positioned read is not supported by the internal stream");
    }
    throttle();
    int readLen = ((PositionedReadable) rawStream).read(position, buffer, offset, length);
    if (readLen != -1) {
      bytesRead += readLen;
    }
    return readLen;
  }
Read bytes starting from the specified position. This requires rawStream is an instance of
{@link PositionedReadable}.
@return the number of bytes read
hbase-common/src/main/java/org/apache/hadoop/hbase/io/hadoopbackport/ThrottledInputStream.java