Subject: Re: 64bit vs 32bit build on amd64
From: Jeff Davis <pgsql@j-davis.com>
To: Roman Krylov <rkrylov@mail.ru>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <44FC8FB4.4030706@mail.ru>
References: <44FC8FB4.4030706@mail.ru>
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Date: Thu, 07 Sep 2006 09:56:01 -0700
Message-Id: <1157648161.20589.154.camel@dogma.v10.wvs>
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On Tue, 2006-09-05 at 00:42 +0400, Roman Krylov wrote:
> Hi.
> My config:
> gentoo linux "2005.1" on amd64x2 in 64-bit mode,
> kernel 2.6.16.12
> glibc 3.3.5(NPTL),
> gcc 3.4.3.
> I had not used portage for building.
> I built two versions of postgres from sources:
> postgresql-8.1.4 native(64bit)
> and 32-bit with CFLAGS=... -m32, and "LD =
> /usr/x86_64-pc-linux-gnu/bin/ld -melf_i386" in src/Makefile.global.
> 32-bit build runs much faster than 64 apparently.
> What benchmark utility should I run to provide more concrete info (numbers)?
> What could be the reason of that difference in performance?
> 

I am also interested in 32-bit versus 64-bit performance. If I only have
4GB of RAM, does it make sense to compile postgresql as a 64-bit
executable? I assume there's no reason for PostgreSQL's shared buffers,
etc., to add up to more than 2GB on a system with 4GB of RAM.

Is there a general consensus on the matter, or is it highly application-
dependent? I am not doing any huge amount of 64-bit arithmetic.

I am using Woodcrest, not Opteron.

Regards,
	Jeff Davis