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From: Mark Wong <markwkm@gmail.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: Andrej Ricnik-Bay <andrej.groups@gmail.com>
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: file system and raid performance
Date: Fri, 8 Aug 2008 09:56:15 -0700
Message-ID: <70c01d1d0808080956p6edd172dgb0125a64fad19265@mail.gmail.com> (raw)
In-Reply-To: <489B727B.6010800@mark.mielke.cc>
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	<489B727B.6010800@mark.mielke.cc>

On Thu, Aug 7, 2008 at 3:08 PM, Mark Mielke <mark@mark.mielke.cc> wrote:
> Andrej Ricnik-Bay wrote:
>
> 2008/8/8 Scott Marlowe <scott.marlowe@gmail.com>:
>
>
> noatime turns off the atime write behaviour.  Or did you already know
> that and I missed some weird post where noatime somehow managed to
> slow down performance?
>
>
> Scott, I'm quite aware of what noatime does ... you didn't miss a post, but
> if you look at Mark's graphs on
> http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide
> they pretty much all indicate that (unless I completely misinterpret the
> meaning and purpose of the labels), independent of the file-system,
> using noatime slows read/writes down (on average)
>
> That doesn't make sense - if noatime slows things down, then the analysis is
> probably wrong.
>
> Now, modern Linux distributions default to "relatime" - which will only
> update access time if the access time is currently less than the update time
> or something like this. The effect is that modern Linux distributions do not
> benefit from "noatime" as much as they have in the past. In this case,
> "noatime" vs default would probably be measuring % noise.

Interesting, now how would we see if it is defaulting to "relatime"?

Regards,
Mark



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