From: James Mansion <james@mansionfamily.plus.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: pgsql-performance@postgresql.org
Subject: Re: POSIX file updates
Date: Mon, 31 Mar 2008 21:41:29 +0100
Message-ID: <47F14C79.2080806@mansionfamily.plus.com> (raw)
In-Reply-To: <47F1436D.4030905@mark.mielke.cc>
References: <47F1413B.40109@mansionfamily.plus.com>
<47F1436D.4030905@mark.mielke.cc>
Mark Mielke wrote:
> Is there anything in POSIX that seems to suggest this? :-) (i.e. why
> are you going under the assumption that the answer is yes - did you
> read something?)
>
It was something somewhere on the Sun web site, relating to tuning Solaris
filesystems. Or databases. Or ZFS. :-(
Needless to say I can't find a search string that finds it now. I
remember being surprised
though, since I wasn't aware of it either.
> I don't believe POSIX has any restriction such as you describe - or if
> it does, and I don't know about it, then most UNIX file systems (if
> not most file systems on any platform) are not POSIX compliant.
That, I can believe.
>
> Linux itself, even without NCQ, might choose to reorder the writes. If
> you use ext2, the pressure to push pages out is based upon last used
> time rather than last write time. It can choose to push out pages at
> any time, and it's only every 5 seconds or so the the system task
> (bdflush?) tries to force out all dirty file system pages. NCQ
> exaggerates the situation, but I believe the issue pre-exists NCQ or
> the SCSI equivalent of years past.
Indeed there do seem to be issues with Linux and fsync. Its one of
things I'm trying to get a
handle on as well - the relationship between fsync and flushes of
controller and/or disk caches.
>
> The rest of your email relies on the premise that POSIX enforces such
> a thing, or that systems are POSIX compliant. :-)
>
True. I'm hoping someone (Jignesh?) will be prompted to remember.
It may have been something in a blog related to ZFS vs other
filesystems, but so far I'm coming
up empty in google. doesn't feel like something I imagined though.
James
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To: pgsql-performance@postgresql.org
Cc: james@mansionfamily.plus.com, mark@mark.mielke.cc
Subject: Re: POSIX file updates
In-Reply-To: <47F14C79.2080806@mansionfamily.plus.com>
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