Feedback-ID: id4a34324:Fastmail
Date: Tue, 24 Mar 2026 23:29:52 -0400
From: Andres Freund <andres@anarazel.de>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	shihao zhong <zhong950419@gmail.com>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Fixes inconsistent behavior in vacuum when it processes multiple
 relations
Message-ID: <loig4i4hc4vuybn6uv6e2kgqm37sebbzujkrvdf6uhbxq5dsfm@7wbkmucts3eu>
References: <aFl1AB9ofnQrrckV@nathan>
 <aFn82kXgvwKHncs-@paquier.xyz>
 <aFrSlSz9fi47j5Sr@nathan>
 <aFtRd1Q4QuCWcg5k@paquier.xyz>
 <aFwT31Rw-Oj-bgO9@nathan>
 <aGIzjYsRrMCEADc5@paquier.xyz>
 <rzxpxod4c4la62yvutyrvgoyilrl2fx55djaf2suidy7np5m6c@3l2ln476eadh>
 <ab2iXwhRe3fFNPfp@nathan>
 <aglpy2jbnb75vufdx6hqkgokquzmoshcbnuxlcxhum4k7tyi7m@27m4hbxo2u2g>
 <acMGcoUwA9CiPPU1@nathan>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <acMGcoUwA9CiPPU1@nathan>
Archived-At: 
 <https://www.postgresql.org/message-id/loig4i4hc4vuybn6uv6e2kgqm37sebbzujkrvdf6uhbxq5dsfm%407wbkmucts3eu>
Precedence: bulk

Hi,

On 2026-03-24 16:47:30 -0500, Nathan Bossart wrote:
> On Fri, Mar 20, 2026 at 04:32:48PM -0400, Andres Freund wrote:
> > On 2026-03-20 14:39:11 -0500, Nathan Bossart wrote:
> >> On Fri, Mar 20, 2026 at 12:27:49PM -0400, Andres Freund wrote:
> >> > Why wasn't it enough to add const markers and keep passing by pointer?
> >> 
> >> IIRC the idea was to prevent similar problems in the future.
> > 
> > Seems using const VacuumParams *params should suffice for that? I don't think
> > it's particularly likely that we'll accept code that casts the const away and
> > then later get hurt by that.
> > 
> >> To avoid the extra #includes, we could instead use the back-patched version
> >> (e.g., commit 661643deda).
> > 
> > I'd probably not go quite there, at least the params should largely be const,
> > with a local on-stack copy where we do need to modify.
> 
> Here is a first try.

Thanks!


Looks reasonable on a skim.


>  static bool
> -vacuum_rel(Oid relid, RangeVar *relation, VacuumParams params,
> +vacuum_rel(Oid relid, RangeVar *relation, const VacuumParams *params,
>  		   BufferAccessStrategy bstrategy)
>  {
>  	LOCKMODE	lmode;
> @@ -2014,18 +2014,21 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams params,
>  	Oid			save_userid;
>  	int			save_sec_context;
>  	int			save_nestlevel;
> +	VacuumParams params_copy;
>  	VacuumParams toast_vacuum_params;

I'd maybe not name it _copy, but params_local or params_table or such, as
somehow it seems a bit odd to modify the copy. But I can't really explain why
it feels odd.

I wonder if more of the code in the function should be updated to use the
copy, otherwise it seems like it could more easily happen that a part of the
code not using the modified version is moved until after a modification, and
the code author assumes the modifications now have taken effect.

Greetings,

Andres Freund