Connecting to restored cluster can be fraught

[allenap]

Especially after restoring from a backup, it's important to know a database role to use, otherwise it's not actually possible to connect to the database. For example, a cluster created as system user gavin will have a superuser role, by default, also named gavin. If this cluster is restored in another account, say bobby, then pgdo will not be able to connect to the restored cluster.

A superuser role can be determined in single-user mode like so:

$ postgres --single -D cluster postgres \
>   <<< 'select rolname from pg_roles where rolsuper and rolcanlogin' \
>     2> /dev/null | sed 's/^.*\brolname\s*=\s*"\(.*\)".*/\1/p;d'
gavin

(Update: function that does this added as cluster::determine_superuser_role_names.)

so pgdo could use this to guess, but perhaps something more/different can be done to make it Just Work.

Note, this might all be moot if pg_hba.conf doesn't allow local connections, for example.