Re: Vacuum, visibility maps and SKIP_PAGES_THRESHOLD

Pavan Deolasee <pavan.deolasee@gmail.com> writes:
> My statistical skills are limited, but wouldn't that mean that for a
> fairly well distributed write activity across a large table, if there
> are even 3-4% update/deletes, we would most likely hit a
> not-all-visible page for every 32 pages scanned ?

Huh?  With a typical table density of several dozen tuples per page, an
update ratio in that range would mean that just about every page would
have something for VACUUM to do, if the modified tuples are evenly
distributed.  The case where the skip optimization has some use is where
there are large "cold" sections that have no changes at all.

Having said that, I don't know how carefully we tested different values
for SKIP_PAGES_THRESHOLD.
        regards, tom lane