gl(at)lbn(dot)fr writes:
> I'm experiencing a strange problem with PostgreSQL 7.4.9.
> One of my database production servers has 2 large databases, it's still
> possible to connect to them and pass queries, but the pg_database
> system table is empty, which prohibits such actions as dumping the
> databases.
Sounds like XID wraparound. Does vacuuming pg_database make the problem
go away? If so, I'd recommend doing database-wide vacuums in all your
databases ASAP. And then instituting a regular vacuum maintenance schedule.
regards, tom lane