From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Provide a pg_truncate_freespacemap function
Date: Tue, 20 Aug 2024 10:03:58 +0200
Message-ID: <12508648.O9o76ZdvQC@aivenlaptop> (raw)
In-Reply-To: <535627.1721540353@sss.pgh.pa.us>
References: <5446938.Sb9uPGUboI@aivenlaptop>
<8acb1f83-2945-42cf-8795-780c94bbed36@oss.nttdata.com>
<535627.1721540353@sss.pgh.pa.us>
Le dimanche 21 juillet 2024, 07:39:13 UTC+2 Tom Lane a écrit :
> Fujii Masao <masao.fujii@oss.nttdata.com> writes:
> >> Le mercredi 6 mars 2024, 20:28:44 CET Stephen Frost a écrit :
> >>> I agree that this would generally be a useful thing to have.
>
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
useful. I'm withdrawing the patch and will keep it in mind if we encounter
other FSM issues in the future.
Best regards,
--
Ronan Dunklau
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To: pgsql-hackers@postgresql.org
Cc: ronan.dunklau@aiven.io, masao.fujii@oss.nttdata.com, tgl@sss.pgh.pa.us, sfrost@snowman.net, pgsql-hackers@lists.postgresql.org
Subject: Re: Provide a pg_truncate_freespacemap function
In-Reply-To: <12508648.O9o76ZdvQC@aivenlaptop>
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