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Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

From: Michael Clemmons <glassresistor(at)gmail(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Greg Smith <greg(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Subject: Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)
Date: 2009-12-29 03:04:06
Message-ID: 4427a97a0912281904qc90817i4edd6852b26dde7f@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Maybe not crash out but in this situation.
N=0
while(N>=0):
    CREATE DATABASE new_db_N;
Since the fsync is the part which takes the memory and time but is happening
in the background want the fsyncs pile up in the background faster than can
be run filling up the memory and stack.
This is very likely a mistake on my part about how postgres/processes
actually works.
-Michael

On Mon, Dec 28, 2009 at 9:55 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On Tuesday 29 December 2009 03:53:12 Michael Clemmons wrote:
> > Andres,
> > Great job.  Looking through the emails and thinking about why this works
> I
> > think this patch should significantly speedup 8.4 on most any file
> > system(obviously some more than others) unless the system has
> significantly
> > reduced memory or a slow single core. On a Celeron with 256 memory I
> >  suspect it'll crash out or just hit the swap  and be a worse bottleneck.
> >  Anyone have something like this to test on?
> Why should it crash? The kernel should just block on writing and write out
> the
> dirty memory before continuing?
> Pg is not caching anything here...
>
> Andres
>

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