private long calSleepTimeMs() {
    return calSleepTimeMs(bytesRead, maxBytesPerSec,
      EnvironmentEdgeManager.currentTime() - startTime);
  }
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