Re: Autovacuum on sys tables

[Inzamam Shafiq <inzamam.shafiq@xxxxxxxxxxx>]

Thanks Thomas for the response,

It means if I run VACUUM ANALYZE on pg_attribute or pg_class table, it is completely safe? Can you please also please confirm what is meant by "mid-level" vacuum?

Regards,

Inzamam Shafiq

Sr. DBA

---

From: Thomas Boussekey <thomas.boussekey@xxxxxxxxx>
Sent: Sunday, December 18, 2022 4:01 PM
To: Inzamam Shafiq <inzamam.shafiq@xxxxxxxxxxx>
Cc: pgsql-general@xxxxxxxxxxxxxxxxxxxx <pgsql-general@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: Autovacuum on sys tables

 

Hello Inzamam,

Le sam. 17 déc. 2022 à 08:16, Inzamam Shafiq <inzamam.shafiq@xxxxxxxxxxx> a écrit :

Dear Experts,

Hope you are doing well.

I have a question that autovacuum is running on sys tables like pg_class, pg_attribute, is it a normal thing? Further, what is dead tuples are not removed from Autovacuum, can we remove the dead tuples using FULL VACUUMM or pg_repack on sys tables?

pg_repack cannot run on system tables, it will FAIL with an explicit error message explaining the limitation.

Each time you perform DDL operations (CREATE, DROP, ALTER), rows are inserted/updated or deleted into the system tables : pg_class, pg_attribute ...

Autovacuum operations perform "low-level" operations, it can be interesting to perform "middle-level" vacuum with VACUUM ANALYZE... that is not blocking, but will be more a resource-consuming operation than autovacuum.

Performing VACUUM FULL operation will block access to these pillar tables of your database. 

If your application/users can handle it, go ahead! 

At work on this kind of operation, I set a statement_timeout, in order to properly stop the process if it is over a defined amount of time.

Hope this helps,

Thomas

Thank you.

Regards,

Inzamam Shafiq

Sr. DBA