Re: Incorrect formula for SysV IPC parameters

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.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center