docs: 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;
      }