pg_conndefaults
Name
pg_conndefaults -- get connection options and their defaults
Description
   pg_conndefaults returns information about the
   connection options available in pg_connect
   -conninfo and the current default value for each option.
  
Return Value
   The result is a list describing the possible connection options and
   their current default values.  Each entry in the list is a sublist
   of the format:
{optname label dispchar dispsize value}
   where the optname is usable as an option in
   pg_connect -conninfo.