From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: Fujii Masao <masao.fujii@oss.nttdata.com>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephen Frost <sfrost@snowman.net>, pgsql-hackers@lists.postgresql.org
Subject: Re: Provide a pg_truncate_freespacemap function
Date: Tue, 20 Aug 2024 10:03:58 +0200
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Le dimanche 21 juillet 2024, 07:39:13 UTC+2 Tom Lane a =C3=A9crit :
> Fujii Masao <masao.fujii@oss.nttdata.com> writes:
> >> Le mercredi 6 mars 2024, 20:28:44 CET Stephen Frost a =C3=A9crit :
> >>> I agree that this would generally be a useful thing to have.
>=20

Sorry for the late reply, as I was not available during the late summer.

> Personally, I want to push back on whether this has any legitimate
> use-case.  Even if the FSM is corrupt, it should self-heal over
> time, and I'm not seeing the argument why truncating it would
> speed convergence towards correct values.  Worse, in the interim
> where you don't have any FSM, you will suffer table bloat because
> insertions will be appended at the end of the table.  So this
> looks like a foot-gun, and the patch's lack of user-visible
> documentation surely does nothing to make it safer.

> (The analogy to pg_truncate_visibility_map seems forced.
> If you are in a situation with a trashed visibility map,
> you are probably getting wrong query answers, and truncating
> the map will make that better.  But a trashed FSM doesn't
> result in incorrect output, and zeroing it will make things
> worse not better.)

Now that the other patch for self-healing is in, I agree it may not be that=
=20
useful. I'm withdrawing the patch and will keep it in mind if we encounter=
=20
other FSM issues in the future.

Best regards,

=2D-
Ronan Dunklau