code: int sendBackups(Operation op) throws Exception {
          if (!(op instanceof BackupAwareOperation)) {
              return 0;
          }
  
          int backupAcks = 0;
          BackupAwareOperation backupAwareOp = (BackupAwareOperation) op;
          if (backupAwareOp.shouldBackup()) {
              backupAcks = sendBackups0(backupAwareOp);
          }
          return backupAcks;
      }
docs: Sends the appropriate backups. This call will not wait till the backups have ACK'ed.
  
  If this call is made with a none BackupAwareOperation, then 0 is returned.
  
  @param op the Operation to backup.
  @return the number of ACKS required to complete the invocation.
  @throws Exception if there is any exception sending the backups.