Oliver Elphick <olly(at)lfix(dot)co(dot)uk> writes:
> This should cause no problem, because we have no
> cross-database communication; it should be impossible for "george(at)dummy"
> to have any connection with database "test".
Not so; you need look no further than the owner column of pg_database
to find a case where people can see usernames that might be local to
other databases. Group membership lists might well contain users
from multiple databases, too.
regards, tom lane