Re: [ADMIN] pg_class reltuples/relpages not updated by autovacuum/vacuum

On Wed, May 25, 2011 at 1:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> I agree that if VACUUM scanned 99% of the table, it's probably fine to
> use its numbers.  It's also fine to use the numbers from ANALYZE,
> because those pages are chosen randomly.  What bothers me is the idea
> of using a small *non-random* sample, and I'm not sure that
> incorporating possibly-bogus results slowly is any better than
> incorporating them quickly.

In particular, unless I'm misremembering, VACUUM *always* scans the
first few pages of the table, until it sees enough consecutive
all-visible bits that it decides to start skipping. If I'm right
about that, then those pages could easily end up being overweighted
when VACUUM does the counting; especially if ANALYZE or an actual
full-table vacuum aren't allowed to snap the count back to reality.

--
Robert Haas
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