Re: -F option, RAM usage, more...

Hmm, it seems we all know just enough to be dangerous :-)

I have seen many threads on the "to fsync() or not to fsync()" and
overwhelmingly people have come out and said that to not fsync() is A Bad
Thing(TM).  -- If Neil is right then it being bad or not is going to depend
very much on the filesystem (I think)...

Now I'm pretty confused (as I'm sure others are) -- can someone that knows
beyond a reasonable doubt beat us with a clue stick on this?  Are we taking
a huge risk if we use -F and disable fsync() or no?

-Mitch

----- Original Message -----
From: "Neil Conway" <nconway@klamath.dyndns.org>
To: <pgsql-general@hub.org>
Sent: Wednesday, October 04, 2000 1:24 PM
Subject: Re: [GENERAL] -F option, RAM usage, more...
On Wed, Oct 04, 2000 at 02:09:47PM -0400, Mike Biamonte wrote:
> I understand from the docs that -F ".. prevents fsync()'s from
> flushing to disk after every transaction.." and that this boosts
> performance because RAM accesses are far faster than disk accesses.  I
> have also seen some impressive stats regarding the degree of this
> performance boost.

Correct me if I'm wrong, but I believe that when you specify '-F', it
allows the filesystem to buffer I/O operations, performing several
operations once after another. This is much faster than with fsync(),
where the disk heads have to be moved frequently. Also, allowing the
I/O subsystem to buffer some data will speed subsequent accesses of it,
until the buffer is flushed.

HTH,

Neil

--
Neil Conway <neilconway@home.com>
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Encrypted mail welcomed

Violence is to dictatorship as propaganda is to democracy.
        -- Noam Chomsky