First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.
Second, the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use (ifx_close() will not close links established by ifx_pconnect()).
This type of links is therefore called 'persistent'.
All of the arguments are optional, and if they're missing, defaults are
taken from values supplied in
php.ini (ifx.default_host for the host
(Informix libraries will use
value if not defined), ifx.default_user for user, ifx.default_password for
the password (none if not defined).
The database name, as a string.
The username, as a string.
The password, as a string.