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Re: synchronous commit vs. hint bits

From: Andres Freund <andres(at)anarazel(dot)de>
To: pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: YAMAMOTO Takashi <yamt(at)mwd(dot)biglobe(dot)ne(dot)jp>, simon(at)2ndquadrant(dot)com
Subject: Re: synchronous commit vs. hint bits
Date: 2011-12-01 09:09:06
Message-ID: 201112011009.06587.andres@anarazel.de (view raw or flat)
Thread:
Lists: pgsql-hackers
Hi Robert, 
On Wednesday, November 30, 2011 02:10:00 PM Robert Haas wrote:
> On Wed, Nov 30, 2011 at 1:37 AM, YAMAMOTO Takashi
> 
> <yamt(at)mwd(dot)biglobe(dot)ne(dot)jp> wrote:
> >> Yes, I would expect that.  What kind of increase are you seeing?  Is
> >> it causing a problem for you, or are you just making an observation?
> > 
> > i was curious because my application uses async commits mainly to
> > avoid frequent fsync.  i have no numbers right now.
> Oh, that's interesting.  Why do you want to avoid frequent fsyncs?  I
> thought the point of synchronous_commit=off was to move the fsyncs to
> the background, but not necessarily to decrease the frequency.
Is that so? If it wouldn't avoid fsyncs how could you reach multiple thousand 
TPS in a writing pgbench run on a pretty ordinary system with fsync=on?

Andres

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