John Sidney-Woollett <johnsw(at)wardbrook(dot)com> writes:
> I decided to switch over to the slave which is now our live database.
> the old master with the problem has already been re-inited (although I
> have a cold backup of the data dir), plus dump files that I can restore
> from.
You panicked much too quickly and destroyed the evidence ... unless by
"cold backup" you mean a filesystem backup, in which case what you
should do is restore that and take a look at what's in its pg_database.
I think there's no question that there is some omission in your vacuuming
procedures, and you need to find out what it is.
regards, tom lane