Re: vacuumdb --analyze-in-stages

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, October 19th, 2021 at 01:02, Euler Taveira <euler@eulerto.com> wrote:

> 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.

Given all the suggestions I've tried to combine them into one patch again.

Regards,

Nikolai