Re: allow changing autovacuum_max_workers without restarting

On Thu, Apr 18, 2024 at 05:05:03AM +0000, Imseih (AWS), Sami wrote:
> I looked at the patch set. With the help of DEBUG2 output, I tested to ensure
> that the the autovacuum_cost_limit  balance adjusts correctly when the 
> autovacuum_max_workers value increases/decreases. I did not think the 
> patch will break this behavior, but it's important to verify this.

Great.

> 1. A nit. There should be a tab here.
> 
> -       dlist_head      av_freeWorkers;
> +       dclist_head av_freeWorkers;

I dare not argue with pgindent.

> 2. autovacuum_max_worker_slots documentation:
> 
> +       <para>
> +        Note that the value of <xref linkend="guc-autovacuum-max-workers"/> is
> +        silently capped to this value.
> +       </para>
> 
> This comment looks redundant in the docs, since the entry 
> for autovacuum_max_workers that follows mentions the
> same.

Removed in v2.  I also noticed that I forgot to update the part about when
autovacuum_max_workers can be changed.  *facepalm*

> 3. The docs for autovacuum_max_workers should mention that when
> the value changes, consider adjusting the autovacuum_cost_limit/cost_delay. 
> 
> This is not something new. Even in the current state, users should think about 
> these settings. However, it seems even important if this value is to be 
> dynamically adjusted.

I don't necessarily disagree that it might be worth mentioning these
parameters, but I would argue that this should be proposed in a separate
thread.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com