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RE: [HACKERS] Re: Max backend limits cleaned up

From: "Daryl W(dot) Dunbar" <daryl(at)www(dot)com>
To: "Bruce Momjian" <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: <tgl(at)sss(dot)pgh(dot)pa(dot)us>, <pgsql-hackers(at)postgreSQL(dot)org>
Subject: RE: [HACKERS] Re: Max backend limits cleaned up
Date: 1999-02-22 17:13:10
Message-ID: 001601be5e86$9f92a8d0$ (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
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.


> -----Original Message-----
> From: Bruce Momjian [mailto:maillist(at)candle(dot)pha(dot)pa(dot)us]
> Sent: Monday, February 22, 1999 11:57 AM
> To: Daryl W. Dunbar
> Cc: tgl(at)sss(dot)pgh(dot)pa(dot)us; pgsql-hackers(at)postgreSQL(dot)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                        |
>   maillist(at)candle(dot)pha(dot)pa(dot)us
>        |  (610) 853-3000
>   +  If your life is a hard drive,     |  830 Blythe Avenue
>   +  Christ can be your backup.        |  Drexel Hill,
> Pennsylvania 19026

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Subject: Re: Anyone understand shared-memory space usage?
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