@Override
  public long getDeadline(RequestHeader header, Message param) {
    if (param instanceof ScanRequest) {
      ScanRequest request = (ScanRequest) param;
      if (!request.hasScannerId()) {
        return 0;
      }

      // get the 'virtual time' of the scanner, and applies sqrt() to get a
      // nice curve for the delay. More a scanner is used the less priority it gets.
      // The weight is used to have more control on the delay.
      long vtime = rpcServices.getScannerVirtualTime(request.getScannerId());
      return Math.round(Math.sqrt(vtime * scanVirtualTimeWeight));
    }
    return 0;
  }
Based on the request content, returns the deadline of the request.
@return Deadline of this request. 0 now, otherwise msec of 'delay'
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSAnnotationReadingPriorityFunction.java