An asynchronous communication method is one in which the application returns control without waiting for a response from the database, and PQsetnonblocking() is used to asynchronize completion of transmission or completion of receipt of all results. Instead of using a function like PQexec(), use a function like PQsendQuery(). In this method, the user application monitors the socket that connects to the database returned by PQsocket(), for example, by using the poll() system call.

For example, if the link to the database goes down, simply monitoring the socket returned by PQsocket() with the poll() system call will not detect it.

However, it is possible to detect the reception of database anomaly detection packets sent from the conmgr process, for example, by monitoring the reception of data on the socket (POLLIN) connecting to the conmgr process returned by PQcmSocket(). Once a reception is detected, the user application need not directly manipulate the packet. By calling something like PQgetResult() or PQcosumeInput() according to the existing application logic, it behaves as if the connection were disconnected. Refer to "Errors when an Application Connection Switch Occurs and Corresponding Actions" in the Application Development Guide on SQLSTATE returned,etc. If you are not using the Connection Manager, PQcmSocket() returns -1.