Date: Wed, 6 Mar 2024 14:28:44 -0500
From: Stephen Frost <sfrost@snowman.net>
To: Ronan Dunklau <ronan.dunklau@aiven.io>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Provide a pg_truncate_freespacemap function
Message-ID: <ZejD7P+i2ZPDw8O/@tamriel.snowman.net>
References: <5446938.Sb9uPGUboI@aivenlaptop>
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Greetings,

* Ronan Dunklau (ronan.dunklau@aiven.io) wrote:
> As we are currently experiencing a FSM corruption issue [1], we need to=
=20
> rebuild FSM when we detect it.=20

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=20
> freespace map, so I propose the attached (liberally copied from the VM=20
> counterpart) to allow to truncate a FSM without incurring downtime, as=20
> currently our only options are to either VACUUM FULL the table or stop th=
e=20
> 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

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