From: Christopher Browne <cbbrowne@acm.org>
Subject: Re: 64-bit vs 32-bit performance ... backwards?
Date: Mon, 12 Jun 2006 22:31:57 -0400
Organization: cbbrowne Computing Inc
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Message-ID: <87bqsx23c2.fsf@wolfe.cbbrowne.com>
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To: pgsql-performance@postgresql.org

anthony@resolution.com (Anthony Presley) wrote:
> Hi all!
>
> I had an interesting discussion today w/ an Enterprise DB developer and
> sales person, and was told, twice, that the 64-bit linux version of
> Enterprise DB (which is based on the 64-bit version of PostgreSQL 8.1)
> is SIGNIFICANTLY SLOWER than the 32-bit version.  Since the guys of EDB
> are PostgreSQL ..... has anyone seen that the 64-bit is slower than the
> 32-bit version?
>
> I was told that the added 32-bits puts a "strain" and extra "overhead"
> on the processor / etc.... which actually slows down the pointers and
> necessary back-end "stuff" on the database.
>
> I'm curious if anyone can back this up .... or debunk it.  It's about
> the polar opposite of everything I've heard from every other database
> vendor for the past several years, and would be quite an eye-opener for
> me.
>
> Anyone?

Traditionally, there has been *some* truth to such assertions.

Consider:

1.  64 bit versions of things need to manipulate 64 bit address values
and such; this will bloat up the code somewhat as compared to 32 bit
versions that will be somewhat more compact.

2.  If you only have 2GB of memory, you get no particular advantage
out of 64 bittedness.

In the days when people had 64 bit Alphas with 256MB of memory, there
was considerable debate about the actual merits of running in 64 bit
mode, and the answers were unobvious.

On the other hand...

3.  Opterons tend to address memory quite a bit quicker than Intels of
pretty much any variety.

4.  64 bit CPUs offer additional registers that can be expected to
make register-bound code quicker.

5.  If you have >>2GB of memory, a 64 bit system is needful to harness
that, and that will make a *big* difference to performance.

The overall claim is somewhat content-free, in the absence of
information about the architecture of the database server.
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