Horton

Re: Move SLRU_PAGES_PER_SEGMENT to pg_config_manual.h

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Andres Freund <andres@anarazel.de>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Maxim Orlov <orlovmg@gmail.com>, Daniil Davydov <3danissimo@gmail.com>, Daniel Gustafsson <daniel@yesql.se>
Date: 2025-11-10T16:24:23Z
Lists: pgsql-hackers 
On 10/11/2025 18:11, Andres Freund wrote:
> Hi,
> 
> On 2025-11-10 13:29:08 +0200, Heikki Linnakangas wrote:
>> At the "make mxidoff 64 bits" thread [1], we're discussing moving
>> SLRU_PAGES_PER_SEGMENT to pg_config_manual.h, to make it accessible from
>> pg_upgrade code. It's currently defined in slru.h, which cannot be included
>> in frontend code. There are many ways we could fix that, but moving
>> SLRU_PAGES_PER_SEGMENT to pg_config_manual.h seems best to me. Patch
>> attached.
> 
> I'm not convinced that pg_config_manual.h is a good place - that suggests it
> makes sense to change the value for some installations, which I don't see any
> reason for. Wouldn't an slrudefs.h or such be more appropriate?

The comment in pg_config_manual.h says about settings defined there:

> In all cases, changing them is only useful in very rare situations
> or for developers.
That seems fitting for SLRU_PAGES_PER_SEGMENT. I don't feel strongly 
either way though, I'm happy to revert and move to slrudefs.h if that's 
the consensus.

I think the control file compatibility check is nice to have in any case 
and we should keep that.

- Heikki

Commits

  1. Add warning to pg_controldata on PG_CONTROL_VERSION mismatch

  2. Add pg_resetwal and pg_controldata support for new control file field

  3. Bump PG_CONTROL_VERSION for commit 3e0ae46d90

  4. Move SLRU_PAGES_PER_SEGMENT to pg_config_manual.h