Date: 22 Jul 2003 20:05:53 +0200 From: Simon J Mudd <sjmudd@pobox.com> To: freebsd-performance@freebsd.org Subject: Re: Tuning for PostGreSQL Database Message-ID: <86znj6l9mm.fsf@unicorn.wl0.org> In-Reply-To: <20030721192643.GD55392@nasby.net> References: <Pine.BSF.4.05.10307191344080.16986-100000@misery.sdf.com> <20030721043501.F14379-100000@walter> <20030721192643.GD55392@nasby.net>
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jim@nasby.net ("Jim C. Nasby") writes:
> > On Sat, 19 Jul 2003, Tom Samplonius wrote:
> > > Softupdates on, async off. Softupdates is just a better async.
> >
> > postgresql fsync's all its files before returning from a commit in order
> > to ensure durability, right? Does softupdates interfere with the
> > functioning of sync(2)/fsync(2)?
>
> No, afaik it only fsync's the write-ahead-logs.
Someone else mentioned Qmail. I use Postfix and I know the author
relies on fsync semantics before confirming the acceptance of email.
I'm sure Qmail (and sendmail, ...) does the same. They should do -
the RFC requires this (that mail can't be lost once it is accepted for
delivery).
Therefore I think we are confusing 2 different issues. The effect of
soft-updates (which tries to reorder writes to ensure FS recover is
easier) and sync/fsync which only returns when the FS or file have
been flushed to disk.
I would guess that PostGreSQL uses fsync() and softupdates do not
effect the fsync() semantics.
Or am I missing something?
Simon
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