Re: PostgreSQL on 64 bit Linux

On Sun, Aug 20, 2006 at 11:00:26PM -0400, Douglas McNaught wrote:
> mark(at)mark(dot)mielke(dot)cc writes:
> > Is there an interest, or any active project to examine PostgreSQL in
> > the area of 64-bit processors? Has it already been done? I don't recall
> > seeing a reference to it in my travels. I'm also not sure on what to
> > expect for results, as the territory is still new. 64-bit processors
> > have existed for a while, but 32-bit processors have been the popular
> > choice, making 64-bit support an after thought?
> I find this question a bit amusing, since PG has run on 64-bit
> architectures such as MIPS, Sparc, Alpha and PA-RISC for quite a while
> now. :)

I don't think so. Software can be designed to take best advantage of
hardware. Recompiling it for a different architecture, running test
cases, and declaring support, is not the same as optimizing for.

> As I said in a private email to Naz, the main advantage I think you'd
> see from 64-bit is the ability to run with more than 2GB or so of
> shared buffers on a system with lots of RAM. Whether you'd want to do
> that, or let the OS do most of the buffering, is an open question...

This is what I mean by after thought. PostgreSQL is designed for
32-bit processors. Which is fine. I'm not complaining. The question
was whether there is an interest in pursuing 64-bit specific
optimizations. In the PostgreSQL code, a quick check points me only to
"has long int 64" as a 64-bit source code #ifdef. Of the six places
that reference this, five of them actually slow down the code, as they
check for overflow of the 'long int' result beyond 4 bytes of
data. The sixth place is used to define the 64-bit type in use by
PostgreSQL, which I suspect is infrequently used.

I believe the answer is no. No or few 64-bit optimization possibilities
have been chased down, probably because some or many of these would:

1) require significant re-architecture

2) reduce the performance in a 32-bit world

It's a question that only half interests me. As with most projects, I
don't think the projects are ready to re-architect for this
purpose. Perhaps once 50%+ of people are running PostgreSQL in 64-bit
mode, the question will be more serious to more people.

As a half interesting question, I'm defending it as a valid question.
Please don't write it off, but it is fine to say "not yet, we have more
important things to work on".

Cheers,
mark

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