Re: Warning about using pg_stat_reset() and pg_stat_reset_shared()

On Wed, Oct  5, 2022 at 11:07:49AM +1300, David Rowley wrote:
> On Thu, 29 Sept 2022 at 04:45, Bruce Momjian <bruce@momjian.us> wrote:
> >
> > We have discussed the problems caused by the use of pg_stat_reset() and
> > pg_stat_reset_shared(), specifically the removal of information needed
> > by autovacuum.  I don't see these risks documented anywhere.  Should we
> > do that?  Are there other risks?
> 
> There was some discussion in [1] a few years back.  A few people were
> for the warning. Nobody seemed to object to it.  There's a patch in
> [2].
> 
> David
> 
> [1] https://www.postgresql.org/message-id/flat/CAKJS1f8DTbCHf9gedU0He6ARsd58E6qOhEHM1caomqj_r9MOiQ%40mail.gmail.com
> [2] https://www.postgresql.org/message-id/CAKJS1f80o98hcfSk8j%3DfdN09S7Sjz%2BvuzhEwbyQqvHJb_sZw0g%40mail.gmail.com

Ah, good point.  I have slightly reworded the doc patch, attached. 
However, the last line has me confused:

    A database-wide <command>ANALYZE</command> is recommended after
    the statistics have been reset.

As far as I can tell, analyze updates pg_statistics values, but not
pg_stat_all_tables.n_dead_tup and n_live_tup, which are used by
autovacuum to trigger vacuum operations.  I am afraid we have to
recommand VACUUM ANALYZE after pg_stat_reset(), no?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson