From: Andres Freund <andres@anarazel.de>
To: pgsql-hackers@postgresql.org
Subject: Re: Large number of open(2) calls with bulk INSERT into empty table
Date: Wed, 7 Dec 2011 02:12:00 +0100
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Cc: Robert Haas <robertmhaas@gmail.com>,
 Florian Weimer <fweimer@bfk.de>
References: <82ipm51tcd.fsf@mid.bfk.de> <827h29q4pd.fsf@mid.bfk.de>
	<CA+TgmobRiGQH+GNC+vTmEf=AgknBirSEUy3PFg4MzpXTXmfLqQ@mail.gmail.com>
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Message-Id: <201112070212.01651.andres@anarazel.de>

On Tuesday, December 06, 2011 08:53:42 PM Robert Haas wrote:
> On Tue, Dec 6, 2011 at 7:12 AM, Florian Weimer <fweimer@bfk.de> wrote:
> > * Robert Haas:
> >> I tried whacking out the call to GetPageWithFreeSpace() in
> >> RelationGetBufferForTuple(), and also with the unpatched code, but the
> >> run-to-run randomness was way more than any difference the change
> >> made.  Is there a better test case?
> > 
> > I think that if you want to exercise file system lookup performance, you
> > need a larger directory, which presumably means a large number of
> > tables.
> 
> OK.  I created 100,000 dummy tables, 10,000 at a time avoid blowing up
> the lock manager.  I then repeated my previous tests, and I still
> can't see any meaningful difference (on my MacBook Pro, running MacOS
> X v10.6.8).  So at least on this OS, it doesn't seem to matter much.
> I'm inclined to defer putting any more work into it until such time as
> someone can demonstrate that it actually causes a problem and provides
> a reproducible test case.  I don't deny that there's probably an
> effect and it would be nice to improve this, but it doesn't seem worth
> spending a lot of time on until we can find a case where the effect is
> measurable.
I think if at all youre going to notice differences at a high concurrency 
because you then would start to hit the price of synchronizing the dcache 
between cpu cores in the kernel.

Andres