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@sra.co.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@hub.org           secondary: scrappy@{freebsd|postgresql}.org