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From: Mark Mielke <mark@mark.mielke.cc>
To: 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: Thu, 07 Aug 2008 18:08:59 -0400
Message-ID: <489B727B.6010800@mark.mielke.cc> (raw)
In-Reply-To: <b35603930808071457x40334261uad77dab2623f2757@mail.gmail.com>
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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.

Cheers,
mark

-- 
Mark Mielke <mark@mielke.cc>

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