This error can occur on either the client or database server side.
When you encounter this error on the client side, it indicates that a network I/O error occurred when the client tried to connect to a database server. Probably the connection attempt timed out because the database server or the network was very busy, too many clients were attempting to connect to the database server simultaneously, or the database server was taken off-line during the connection attempt.
If you are using IBM Informix Dynamic Server, IBM Informix Universal Server, or IBM Informix OnLine Dynamic Server, verify that the database server is still online. If you are using IBM Informix SE, verify that the sqlexecd daemon for the database server is still running. Use either or both of the environment variables INFORMIXCONTIME and INFORMIXCONRETRY on the client side to increase the connection time and number of retry attempts.
When you encounter this error on the database server side, it is a warning that a network I/O error is detected while the database server is accepting a connection request from a client. This error usually occurs when the database server or the network is very busy or when too many clients are trying to connect to the database server at once. The database server might be taking so long to respond to a client that the client's connection request timed out before the connection is complete. Or possibly a client terminated its connection attempt before the connection is completely established.
If this error is seen only occasionally in the server message log, it is just a warning. No corrective action is required on the server side.
If this error occurs frequently on a database server that runs on a host with multiple processors, you might want to tune the database server by increasing the number of poll threads and/or listener threads.