This catalog defines groups and stores what users belong to what
   groups.  Groups are created with the CREATE
   GROUP command.  Consult the Administrator's
   Guide for information about user permission management.
  
   Because user and group identities are cluster-wide,
   pg_group
   is shared across all databases of a cluster: there is only one
   copy of pg_group per cluster, not
   one per database.
  
Table 3-15. pg_group Columns
| Name | Type | References | Description | 
|---|
| groname | name |  | Name of the group | 
| grosysid | int4 |  | An arbitrary number to identify this group | 
| grolist | int4[] | pg_shadow.usesysid | An array containing the ids of the users in this group |