Re: [HACKERS] PostgreSQL and Solaris 7?

As promised, sorry for the delay...

http://sunsolve.Sun.COM/private-cgi/us/doc2html?infodoc/2270+91876015215168

This gives an explnation of it all for Solaris...

On Thu, 11 Feb 1999, Tom Lane wrote:

> Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp> writes:
> > Ok. If I consider 64 backends, at least following settings would be
> > required from your suggestion:
>
> > 64 entries in semaphore map (SEMMAP)
> > 64 semaphore identifiers (SEMMNI)
> > 64 semaphores in system (SEMMNS)
> > 25 max semaphores per id (SEMMSL)
>
> > Is this correct?
>
> No. You do need SEMMNS >= 64 of course, but Postgres only needs a
> sema identifier for each block of 16 semas, so SEMMNI >= 4 will work.
> According to my references, the recommended value of SEMMAP is SEMMNI+2
> (it's for keeping track of unused "holes" between allocated sema-ID
> groups, so that seems like it ought to be enough). SEMMSL could be as
> low as 16, though I see no reason to reduce the default value.
>
> In reality, of course, you had better leave some slop for other Unix
> programs to be able to grab semas of their own. I'd suggest at least
> doubling the minimum SEMMNS and SEMMNI. (On my HP box, ipcs shows
> various root-owned subsystems using 6 sema IDs with a total of 8 semas.
> So I'd need at least SEMMNS = 72, SEMMNI = 10 to run 64 backends ---
> with no margin for error.)
>
> I never understood why the default sema configuration values were so
> small anyway --- it's not like a semaphore uses a huge amount of kernel
> space...
>
> regards, tom lane
>

Marc G. Fournier
Systems Administrator @ hub.org
primary: scrappy(at)hub(dot)org secondary: scrappy(at){freebsd|postgresql}.org