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Re: Changing the default configuration (was Re: [HACKERS] PostgreSQL Benchmarks)

From: Steve Crawford <scrawford(at)pinpointresearch(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,"Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com>
Cc: "PostgresSQL Hackers Mailing List" <pgsql-hackers(at)postgresql(dot)org>,pgsql-advocacy(at)postgresql(dot)org
Subject: Re: Changing the default configuration (was Re: [HACKERS] PostgreSQL Benchmarks)
Date: 2003-02-11 17:10:48
Message-ID: 20030211171048.579E1103F6@polaris.pinpointresearch.com (view raw or flat)
Thread:
Lists: pgsql-advocacypgsql-hackerspgsql-performance
A quick-'n'-dirty first step would be more comments in postgresql.conf. Most 
of the lines are commented out which would imply "use the default" but the 
default is not shown. (I realize this has the difficulty of defaults that 
change depending upon how PostgreSQL was configured/compiled but perhaps 
postgresql.conf could be built by the make process based on the configuration 
options.)

If postgresql.conf were commented with recommendations it would probably be 
all I need though perhaps a recommendation to edit that file should be 
displayed at the conclusion of "make install".

Cheers,
Steve


On Tuesday 11 February 2003 8:20 am, Tom Lane wrote:
> "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> writes:
> > May I make a suggestion that maybe it is time to start thinking about
> > tuning the default config file, IMHO its just a little bit too
> > conservative,
>
> It's a lot too conservative.  I've been thinking for awhile that we
> should adjust the defaults.
>
> The original motivation for setting shared_buffers = 64 was so that
> Postgres would start out-of-the-box on machines where SHMMAX is 1 meg
> (64 buffers = 1/2 meg, leaving 1/2 meg for our other shared data
> structures).  At one time SHMMAX=1M was a pretty common stock kernel
> setting.  But our other data structures blew past the 1/2 meg mark
> some time ago; at default settings the shmem request is now close to
> 1.5 meg.  So people with SHMMAX=1M have already got to twiddle their
> postgresql.conf settings, or preferably learn how to increase SHMMAX.
> That means there is *no* defensible reason anymore for defaulting to
> 64 buffers.
>
> We could retarget to try to stay under SHMMAX=4M, which I think is
> the next boundary that's significant in terms of real-world platforms
> (isn't that the default SHMMAX on some BSDen?).  That would allow us
> 350 or so shared_buffers, which is better, but still not really a
> serious choice for production work.
>
> What I would really like to do is set the default shared_buffers to
> 1000.  That would be 8 meg worth of shared buffer space.  Coupled with
> more-realistic settings for FSM size, we'd probably be talking a shared
> memory request approaching 16 meg.  This is not enough RAM to bother
> any modern machine from a performance standpoint, but there are probably
> quite a few platforms out there that would need an increase in their
> stock SHMMAX kernel setting before they'd take it.
>
> So what this comes down to is making it harder for people to get
> Postgres running for the first time, versus making it more likely that
> they'll see decent performance when they do get it running.
>
> It's worth noting that increasing SHMMAX is not nearly as painful as
> it was back when these decisions were taken.  Most people have moved
> to platforms where it doesn't even take a kernel rebuild, and we've
> acquired documentation that tells how to do it on all(?) our supported
> platforms.  So I think it might be okay to expect people to do it.
>
> The alternative approach is to leave the settings where they are, and
> to try to put more emphasis in the documentation on the fact that the
> factory-default settings produce a toy configuration that you *must*
> adjust upward for decent performance.  But we've not had a lot of
> success spreading that word, I think.  With SHMMMAX too small, you
> do at least get a pretty specific error message telling you so.
>
> Comments?
>
> 			regards, tom lane
>
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