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Re: [GENERAL] Running with fsync=off

From: "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: [GENERAL] Running with fsync=off
Date: 2005-12-28 19:12:54
Message-ID: douo1j$1ja6$1@news.hub.org (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-general
"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote
>
> The actual runtime of the "sync" program is epsilon, because it doesn't
> wait for all the I/O to happen.  The entire reason for the custom is
> that the I/O is going on while you type the second "sync".

But in our 7.4.x, there is code like this:

 sync();
 if (IsUnderPostmaster)
  sleep(2);
 sync();

So for standalone backend, that's just "sync();sync()". So the "I/O is going
on while you type the second sync" theory doesn't work. For ordinary
backends, that's even more wierd - Why wasting 2 seconds is enough to save
the data? Why not 3 seconds or 4?

Regards,
Qingqing




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