I wrote:
> The light just went on ... system catalog updates don't generate
> statistics reports. Hence, autovacuum doesn't know any work is needed.
The above claim is too strong --- they do normally generate stats
updates. However, in a simple test I observed that
pg_stat_all_tables.n_tup_del did not seem to increment for the deletes
that occur when a temp table is dropped during backend exit. (Most
likely we aren't flushing out the final stats messages...)
Steve, is your app in the habit of creating lots of temp tables that are
not dropped explicitly? That would explain why you are getting bit more
than other people.
regards, tom lane