The connection service file allows libpq connection parameters to be
   associated with a single service name. That service name can then be
   specified in a libpq connection string, and the associated settings will be
   used. This allows connection parameters to be modified without requiring
   a recompile of the libpq-using application. The service name can also be
   specified using the PGSERVICE environment variable.
  
   Service names can be defined in either a per-user service file or a
   system-wide file.  If the same service name exists in both the user
   and the system file, the user file takes precedence.
   By default, the per-user service file is named
   ~/.pg_service.conf.
   On Microsoft Windows, it is named
   %APPDATA%\postgresql\.pg_service.conf (where
   %APPDATA% refers to the Application Data subdirectory
   in the user's profile).  A different file name can be specified by
   setting the environment variable PGSERVICEFILE.
   The system-wide file is named pg_service.conf.
   By default it is sought in the etc directory
   of the PostgreSQL installation
   (use pg_config --sysconfdir to identify this
   directory precisely).  Another directory, but not a different file
   name, can be specified by setting the environment variable
   PGSYSCONFDIR.
  
Either service file uses an “INI file” format where the section name is the service name and the parameters are connection parameters; see Section 34.1.2 for a list. For example:
# comment [mydb] host=somehost port=5433 user=admin
   An example file is provided in
   the PostgreSQL installation at
   share/pg_service.conf.sample.
  
   Connection parameters obtained from a service file are combined with
   parameters obtained from other sources.  A service file setting
   overrides the corresponding environment variable, and in turn can be
   overridden by a value given directly in the connection string.
   For example, using the above service file, a connection string
   service=mydb port=5434 will use
   host somehost, port 5434,
   user admin, and other parameters as set by
   environment variables or built-in defaults.