Feedback-ID: i76984098:Fastmail
Message-ID: <6f44101c-ce01-478e-9fb1-138a10f358d9@aklaver.com>
Date: Sun, 16 Feb 2025 08:19:35 -0800
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
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
To: Y_Bharani_mbsv <mailbsv@yahoo.com>,
 Greg Sabino Mullane <htamfids@gmail.com>,
 Ron Johnson <ronljohnsonjr@gmail.com>
Cc: pgsql-general <pgsql-general@postgresql.org>
References: <0558ddd4d71641bdb41fa49b2425f73c@safrangroup.com>
 <CANzqJaC1Uk4H=55vV_jbFYMuD1f9Bb_4Y9WKvkZA3bt92bEUnw@mail.gmail.com>
 <498dfb34-4dd7-4f48-8188-355e1488d7e6@aklaver.com>
 <1061066336.5835157.1733316137292@mail.yahoo.com>
 <CAKAnmmKZdhnhdNRd3OgDyEco9OPkT=qA_TeWMFMRvUM9pXauKg@mail.gmail.com>
 <1482982714.8486017.1735661703839@mail.yahoo.com>
 <1763130721.4001842.1737733841628@mail.yahoo.com>
 <c3fc88ef-d155-4455-bc01-2c569b401998@aklaver.com>
 <132487461.4068668.1737741687606@mail.yahoo.com>
 <0dc06cb7-33cc-43ba-a95f-535fdf0a0439@aklaver.com>
 <1751608443.5432365.1738081421269@mail.yahoo.com>
 <74599d1d-c8a2-4e59-a50d-019dcc973de8@aklaver.com>
 <200665967.5560583.1738095230696@mail.yahoo.com>
 <21b5d62a-19d1-413f-9d5e-d681cd2bb91b@aklaver.com>
 <47454513.6047834.1738179914107@mail.yahoo.com>
 <1841861276.9581730.1738888679871@mail.yahoo.com>
 <fabc9547-1de0-4efa-baf5-124d91e3fab5@aklaver.com>
 <56243553.9616888.1738893835649@mail.yahoo.com>
 <940531722.732202.1739711614045@mail.yahoo.com>
Content-Language: en-US
From: Adrian Klaver <adrian.klaver@aklaver.com>
In-Reply-To: <940531722.732202.1739711614045@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: <https://www.postgresql.org/message-id/6f44101c-ce01-478e-9fb1-138a10f358d9%40aklaver.com>
Precedence: bulk

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.klaver@aklaver.com