Re: allow changing autovacuum_max_workers without restarting

>>> That's true, but using a hard-coded limit means we no longer need to add a
>>> new GUC. Always allocating, say, 256 slots might require a few additional
>>> kilobytes of shared memory, most of which will go unused, but that seems
>>> unlikely to be a problem for the systems that will run Postgres v18.
>>
>> I agree with this.


> Here's what this might look like. I chose an upper limit of 1024, which
> seems like it "ought to be enough for anybody," at least for now.

I thought 256 was a good enough limit. In practice, I doubt anyone will 
benefit from more than a few dozen autovacuum workers. 
I think 1024 is way too high to even allow.

Besides that the overall patch looks good to me, but I have
some comments on the documentation.

I don't think combining 1024 + 5 = 1029 is a good idea in docs.
Breaking down the allotment and using the name of the constant 
is much more clear.

I suggest 
" max_connections + max_wal_senders + max_worker_processes + AUTOVAC_MAX_WORKER_SLOTS + 5"

and in other places in the docs, we should mention the actual 
value of AUTOVAC_MAX_WORKER_SLOTS. Maybe in the 
below section?

Instead of:
-    (<xref linkend="guc-autovacuum-max-workers"/>) and allowed background
+    (1024) and allowed background

do something like:
-    (<xref linkend="guc-autovacuum-max-workers"/>) and allowed background
+   AUTOVAC_MAX_WORKER_SLOTS  (1024) and allowed background

Also,  replace the 1024 here with AUTOVAC_MAX_WORKER_SLOTS.

+    <varname>max_wal_senders</varname>,
+    plus <varname>max_worker_processes</varname>, plus 1024 for autovacuum
+    worker processes, plus one extra for each 16


Also, Not sure if I am mistaken here, but the "+ 5" in the existing docs
seems wrong.
 
If it refers to NUM_AUXILIARY_PROCS defined in 
include/storage/proc.h, it should a "6"

#define NUM_AUXILIARY_PROCS             6

This is not a consequence of this patch, and can be dealt with
In a separate thread if my understanding is correct.


Regards,

Sami