Message-ID: <a578eba3-7242-4450-aa2c-acedeb08dc93@iki.fi>
Date: Fri, 6 Mar 2026 16:43:24 +0200
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Subject: Re: Rework SLRU I/O errors handle
To: Maxim Orlov <orlovmg@gmail.com>,
 Postgres hackers <pgsql-hackers@lists.postgresql.org>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
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On 26/02/2026 16:26, Maxim Orlov wrote:
> Beginning of the discussion is here [0].
> 
> Historically, the SLRU module was designed to handle 32-bit
> transactions. However, it is now utilised for handling a variety of
> object types, like TransactionId, MultixactId, MultiXactOffset,
> QueuePosition, and so on. But the IO error reporting system is still
> designed to support 32-bit XIDs exclusively.
> 
> The proposed patchset allows us to define a "custom" callback to
> improve error messages.
> 
> The first two commits add a callback and test case. The subsequent ones
> improve I/O error messages. The last one adds the XID epoch to the error
> message. It's purely optional, but I think it would be useful.
> 
> [0] https://www.postgresql.org/message-id/ 
> CACG%3Dezbwy1zargXDNPeYXxZwRW3jXu_aD%3DrcG-7dc4fw7Y9Ojw%40mail.gmail.com 
> <https://www.postgresql.org/message-id/ 
> CACG%3Dezbwy1zargXDNPeYXxZwRW3jXu_aD%3DrcG-7dc4fw7Y9Ojw%40mail.gmail.com>

Thanks, looks reasonable.

I'm -1 on the last patch, "Expand xact SLRU IO-error to show epoch" 
though. The epoch isn't used in addressing the SLRU, the patch just 
expands the 32-bit XID into a full 64-bit XID using the current epoch. 
That seems misleading.

- Heikki