I wrote:
> So this *should* have resulted in the stats file shrinking. Did you
> happen to notice if it did, after you did this?
Oh, never mind that --- I can see that it did shrink, just from counting
the write() calls in the collector's strace. So what we have here is a
demonstration that the tabpurge mechanism does work for you, when it's
invoked. Which is further evidence that for some reason autovacuum is
not running for you.
What I'd suggest at this point is cranking up log_min_messages to DEBUG2
or so in postgresql.conf, restarting the postmaster, and keeping an eye
on the log to see if you can spot anything about why autovac isn't
working.
regards, tom lane