Re: postgresql 18 and shm

[Greg Troxel <gdt%lexort.com@localhost>]

Marc Baudoin <babafou%babafou.eu.org@localhost> writes:

> Greg Troxel <gdt%lexort.com@localhost> écrit :
>> 
>> Reading pgsql 17 docs
>
> 18 ?

sorry, I read both

>> It would be great if you can read the docs closely and understand all
>> the components that make up semaphore use, to see if things are as we'd
>> expect.  I don't understand why you need semmni so high, from reading.
>
> I got my values from trial and error:
>
> https://mail-index.netbsd.org/pkgsrc-users/2025/10/26/msg042118.html
>
> The minimum values that make PostgreSQL 18 run are (on the system
> I tested last year) are:
>
> kern.ipc.semmni=11
> kern.ipc.semmns=187
>
> So I rounded up to get:
>
> kern.ipc.semmni=20
> kern.ipc.semmns=200

The pgsql 18 docs give formulas in terms of adding other variables, and
give an invocation to print them.  One can trace the formulas and see if
that gets the same result as your experiment.