Re: Help in vetting outcome of "vacuumdb --analyze-in-stages" - during DB Upgrade from EC2- PGS - Community Edn ver 13.X to 14.X

On 2/16/25 05:13, Y_Bharani_mbsv wrote:
> Team
> Good Morning.
> As part of DB upgrade from EC2 - PGS - community Edn Ver 13.X to 14.X
> I followed steps of "pg_upgrade" and had executed the last step (post
> successful db migration)
>
> vacuumdb --analyze-in-stages
>
> and later noticed an caveat
> url = https://www.postgresql.org/docs/current/app-vacuumdb.html
> <https://www.postgresql.org/docs/current/app-vacuumdb.html>
>
>
> |--analyze-in-stages|
>
> Only calculate statistics for use by the optimizer (no vacuum), like
> |--analyze-only|. Run three stages of analyze; the first stage uses
> the lowest possible statistics target (see default_statistics_target
> <https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-DEFAULT-STATISTICS-TARGET>) to produce usable statistics faster, and subsequent stages build the full statistics.
>
> This option is only useful to analyze a database that currently has
> no statistics or has wholly incorrect ones, such as if it is newly
> populated from a restored dump or by |pg_upgrade|. *Be aware that
> running with this option in a database with existing statistics may
> cause the query optimizer choices to become transiently worse due to
> the low statistics targets of the early stages.*

Did you skip over reading this part?:

"This option is only useful to analyze a database that currently has no
statistics or has wholly incorrect ones, such as if it is newly
populated from a restored dump or by pg_upgrade."

>
>
> How to overcome the issue to avoid "transiently worse"
>
>
>
>   Later, I too did
> a) vacuum(full,verbose,skip_locked) ... each table wise
> b) analyze (verbose,skip_locked) .. each table wise
> Any guidance
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com