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Re: mosbench revisited

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: mosbench revisited
Date: 2011-08-03 18:41:29
Message-ID: 20110803184128.GC24821@svana.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Aug 03, 2011 at 02:21:25PM -0400, Robert Haas wrote:
> It would be nice if the Linux guys would fix this problem for us, but
> I'm not sure whether they will.  For those who may be curious, the
> problem is in generic_file_llseek() in fs/read-write.c.  On a platform
> with 8-byte atomic reads, it seems like it ought to be very possible
> to read inode->i_size without taking a spinlock.

Interesting. There's this thread from 2003 suggesting the use of pread
instead, it was rejected on the argument that lseek is cheap so not a
problem.

http://archives.postgresql.org/pgsql-patches/2003-02/msg00197.php

Perhaps we now have a benchmark where the effect can be measured.

There's the issue about whether it screws up the readahead mechanism...

Have a nice day,
-- 
Martijn van Oosterhout   <kleptog(at)svana(dot)org>   http://svana.org/kleptog/
> He who writes carelessly confesses thereby at the very outset that he does
> not attach much importance to his own thoughts.
   -- Arthur Schopenhauer

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