Re: Incorrect formula for SysV IPC parameters

On Fri, Feb 12, 2016 at 11:19 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Fri, Feb 5, 2016 at 2:17 PM, Kyotaro HORIGUCHI
> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> At Thu, 4 Feb 2016 21:43:04 +0900, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote in <CAHGQGwHgBsat29_ZqK3aXg4a5Lsa0JUv579VkGWX3R_g0KOncw(at)mail(dot)gmail(dot)com>
>>> On Wed, Feb 3, 2016 at 12:51 PM, Kyotaro HORIGUCHI
>>> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> > Hello, I found that the formulas to calculate SEMMNI and SEMMNS
>>> > are incorrect in 9.2 and later.
>>> >
>>> > http://www.postgresql.org/docs/9.5/static/kernel-resources.html
>>> >
>>> > But actually the number of semaphores PostgreSQL needs is
>>> > calculated as following in 9.4 and later.
>> ...
>>> > So, the formula for SEMMNI should be
>>> >
>>> > ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)
>>> >
>>> > and SEMMNS should have the same fix.
>>> >
>>> >
>>> > In 9.3 and 9.2, the documentation says the same thing but
>> ...
>>> > ceil((max_connections + autovacuum_max_workers + 5) / 16)
>>> >
>>> > In 9.1, NUM_AUXILIARY_PROCS is 3 so the documentations is correct.
>>>
>>> Good catch!
>>
>> Thanks.
>>
>>> 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?

Pushed. Thanks for the report and patches!

Regards,

--
Fujii Masao