Re: vacuumdb --analyze-in-stages

On Mon, Oct 18, 2021, at 8:53 PM, Alvaro Herrera wrote:
> On 2021-Oct-18, David G. Johnston wrote:
> 
> > On Mon, Oct 18, 2021 at 4:02 PM Alvaro Herrera <alvherre@alvh.no-ip.org>
> > wrote:
> 
> > > Given that the first stage uses statistic target=1, running this option
> > > in a database with any stats at all is probably a bad idea.
> >
> > Add the word "only"?
> > 
> > This option is only useful to analyze a database...
> 
> Maybe this is sufficient, since it would drive people away from trying
> to do anything else than help upgrades with it.
+1. I like your 2nd suggestion.

"This option is only useful to analyze a database that was newly populated from
a restored dump or by <command>pg_upgrade</command>.  Beware that running with
this option in a database with existing statistics may cause query optimizer
choices to become transiently worse, because of the very low statistics target
that is used in the early stages."

> 
> > "Run several (currently three) stages of analyze with different
> > configuration settings, to produce usable statistics faster.  The first of
> > these stages will remove any existing statistics even if they use a larger
> > statistic target configuration."
> 
> .. yeah, this is another option.
We might include it too but I would suggest "replace" instead of "remove"
because it seems there won't be statistics after the first stage.


--
Euler Taveira
EDB   https://www.enterprisedb.com/