Date: Fri, 22 Sep 2006 14:52:09 +1200
From: Guy Thornley <guy@esphion.com>
To: Markus Schaber <schabi@logix-tt.com>
Cc: Luke Lonergan <llonergan@greenplum.com>, pgsql-performance@postgresql.org
Subject: Re: Large tables (was: RAID 0 not as fast as
Message-ID: <20060922025209.GO6211@esphion.com>
Reply-To: Guy Thornley <guy@esphion.com>
References: <C1372993.2361%llonergan@greenplum.com>
	<45123FC0.9060100@logix-tt.com>
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> >> I thought that posix_fadvise() with POSIX_FADV_WILLNEED was exactly
> >> meant for this purpose?
> > 
> > This is a good idea - I wasn't aware that this was possible.
> 
> This possibility was the reason for me to propose it. :-)

posix_fadvise() features in the TODO list already; I'm not sure if any work
on it has been done for pg8.2.

Anyway, I understand that POSIX_FADV_DONTNEED on a linux 2.6 kernel allows
pages to be discarded from memory earlier than usual. This is useful, since
it means you can prevent your seqscan from nuking the OS cache.

Of course you could argue the OS should be able to detect this, and prevent
it occuring anyway. I don't know anything about linux's behaviour in this
area.

.Guy