The default to-date has been 64. The reason you don't see much
trouble with it is twofold, 1) Linux has a huge default for
semaphores and shared memory, 2) The old memory model allocated
semaphores in blocks of 16 up to MaxBackedId (which was hard coded
to 64). I did not run into trouble on untuned Solaris until
postmaster tried to start the 49th backend (semaphores 49-64 when my
kernel defaulted to 60).
The new model allocates semaphores and shared memory at startup,
assuring you won't experience midstream troubles like I did. It
does, however allocate to the max or -N setting, which most users
will probably never reach.
I'd vote for 32 as the default.
DwD
> -----Original Message-----
> From: Bruce Momjian [mailto:maillist@candle.pha.pa.us]
> Sent: Monday, February 22, 1999 11:57 AM
> To: Daryl W. Dunbar
> Cc: tgl@sss.pgh.pa.us; pgsql-hackers@postgreSQL.org
> Subject: Re: [HACKERS] Re: Max backend limits cleaned up
>
>
> [Charset iso-8859-1 unsupported, filtering to ASCII...]
> > Having recently experienced a similar problem with
> semaphores and
> > kernel size, I can say it is an issue. I feel that
> documentation
> > will clear it up either way. Either you lower the
> default backend
> > limit, and document how to raise it along with the
> associated kernel
> > variables, or leave it alone and document the
> appropriate steps to
> > tuning the kernel to accommodate it and how to lower it
> if you don't
> > want to tune the kernel.
> >
>
> The issue for me is that novices who are never going to
> hit the 32-user
> limit should be able to install PostgreSQL with no major changes,
> including not even a postmaster flag to lower the limit.
>
> If you need more than 32 connections, you will be able to
> modify the
> kernel.
>
> --
> Bruce Momjian |
> http://www.op.net/~candle
> maillist@candle.pha.pa.us
> | (610) 853-3000
> + If your life is a hard drive, | 830 Blythe Avenue
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>