How to remove freezes on the server using select?

Question

C++ / C#

I wrote a proxy server. The server is single-threaded, it works through select. I have a piece of code that blocks the server:

bool closeConnect = false;
  std::string req = _getReq(closeConnect, fd);
  try {
    _dbSock->init();
    _dbSock->connectTo();
  } catch (std::exception &e) {
    std::cerr << "DB sock: " << e.what() << std::endl;
    closeConnect = true;
  }
  if (!closeConnect) {
    send(_dbSock->getSocket(), req.c_str(), req.size(), 0);
    bool tmp;
    req.erase();
    req = _getReq(tmp, _dbSock->getSocket());
    std::cerr << req.size();
    send(fd, req.c_str(), req.length(), 0);
  }

I know that it is blocked at the moment of communication with the database, but I don’t understand how to fix it? I tried first to open a socket for the db, and add it to fd_set, but, most likely, I did it somehow wrong, because in general everything stopped working.