Re: Incorrect formula for SysV IPC parameters

On Mon, Feb 15, 2016 at 2:31 PM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> Thanks for looking at this.
>
> At Fri, 12 Feb 2016 23:19:45 +0900, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote in <CAHGQGwHEnT+-S+axWKQPBYSg6z852OfgS6gDXi0Ycpq5QW=iww(at)mail(dot)gmail(dot)com>
>> >> ISTM that you also need to change the descriptions about SEMMNI and SEMMNS
>> >> under the Table 17-1.
>> >
>> > Oops! Thank you for pointing it out.
>> >
>> > The original description doesn't mention the magic-number ('5' in
>> > the above formulas, which previously was '4') so I haven't added
>> > anything about it.
>> >
>> > Process of which the number is limited by max_worker_processes is
>> > called 'background process' (not 'backend worker') in the
>> > documentation so I used the name to mention it in the additional
>> > description.
>> >
>> > The difference in the body text for 9.2, 9.3 is only a literal
>> > '4' to '5' in the formula.
>>
>> Thanks for updating the patches!
>>
>> They look good to me except that the formulas don't include the number of
>> background processes requesting shared memory access, i.e.,
>> GetNumShmemAttachedBgworkers(), in 9.3. Isn't it better to use the following
>> formula in 9.3?
>>
>> ceil((max_connections + autovacuum_max_workers + number of
>> background proceses + 5) / 16)
>>
>> Attached patch uses the above formula for 9.3. I'm thinking to push your
>> patches to 9.2, 9.4, 9.5, master, also push the attached one to 9.3.
>> Comments?
>
> One concern is that users don't have any simple way to know how
> many bg-workers a server runs in their current configuration.

Users need to read the document of the extensions they want to load,
to see the number of background worker processes which will be running.

> The formula donsn't make sense without it.

IMO, documenting "incorrect" formula can cause more troubles.

Regards,

--
Fujii Masao