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@xxxxxxxxxxx
