In psql \d+, display oids only when they exist, and display replication
identity only when it is non-default. Also document the defaults for
replication identity for system and non-system tables. Update
regression output.
Display "replica identity" only for \d plus mode, exclude system schema
objects, and display all possible values, not just non-default,
non-index ones.
Pending patches for logical replication will use this to determine
which columns of a tuple ought to be considered as its candidate key.
Andres Freund, with minor, mostly cosmetic adjustments by me