Re: Update maintenance_work_mem/autovacuum_work_mem to reflect the 1GB limitation with VACUUM

On Fri, 2021-07-02 at 23:31 +1200, David Rowley wrote:
> I had a look at the patch in [1] and I find it a bit weird that we'd
> write the following about autovacuum_work_mem in our docs:
> 
> +       <para>
> +        Note that <command>VACUUM</command> has a hard-coded limit of 1GB
> +        for the amount of memory used, so setting
> +        <varname>autovacuum_work_mem</varname> higher than that has no effect.
> +       </para>
> 
> Since that setting is *only* used for auto vacuum, why don't we just
> limit the range of the GUC to 1GB?
> 
> Of course, it wouldn't be wise to backpatch the reduced limit of
> autovacuum_work_mem as it might upset people who have higher values in
> their postgresql.conf when their database fails to restart after an
> upgrade. I think what might be best is just to reduce the limit in
> master and apply the doc patch for just maintenance_work_mem in all
> supported versions. We could just ignore doing anything with
> autovacuum_work_mem in the back branches and put it down to a
> historical mistake that can't easily be fixed now.
> 
> I've attached what I came up with.
> 
> What do you think?
> 
> [1] https://www.postgresql.org/message-id/514fe5ce4714b7b33cb0a611f0c7b72df413bef5.camel%40cybertec.at

I think that is much better.
I am fine with that patch.

Yours,
Laurenz Albe