Subject: Re: Provide a pg_truncate_freespacemap function

From: Stephen Frost <[email-masked]>
Date: Wed, 6 Mar 2024 14:28:44 -0500

Greetings,

* Ronan Dunklau ([email-masked]) wrote:
> As we are currently experiencing a FSM corruption issue [1], we need to 
> rebuild FSM when we detect it. 

Ideally, we'd figure out a way to pick up on this and address it without
the user needing to intervene, however ...

> I noticed we have something to truncate a visibility map, but nothing for the 
> freespace map, so I propose the attached (liberally copied from the VM 
> counterpart) to allow to truncate a FSM without incurring downtime, as 
> currently our only options are to either VACUUM FULL the table or stop the 
> cluster and remove the FSM manually.

I agree that this would generally be a useful thing to have.

> Does that seem correct ?

Definitely needs to have a 'REVOKE ALL ON FUNCTION' at the end of the
upgrade script, similar to what you'll find at the bottom of
pg_visibility--1.1.sql in the tree today, otherwise anyone could run it.

Beyond that, I'd suggest a function-level comment above the definition
of the function itself (which is where we tend to put those- not at the
point where we declare the function).

Thanks!

Stephen