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From: Adrian Klaver <[email protected]>
To: Y_Bharani_mbsv <[email protected]>
To: Greg Sabino Mullane <[email protected]>
To: Ron Johnson <[email protected]>
Cc: pgsql-general <[email protected]>
Subject: Re: Help in vetting outcome of "vacuumdb --analyze-in-stages" - during DB Upgrade from EC2- PGS - Community Edn ver 13.X to 14.X
Date: Sun, 16 Feb 2025 08:19:35 -0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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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
[email protected]

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