Re: x86-64 and PostgreSQL

On Mon, 2003-01-20 at 00:29, Shridhar Daithankar wrote:
> On 18 Jan 2003 at 11:39, Andrew Sullivan wrote:
> > On Fri, Jan 17, 2003 at 11:29:25PM -0600, Ron Johnson wrote:
> > > Hi,
> > >
> > > Will there be any advantages to running Pg on a 64-bit CPU rather
> > > than 32-bit?
> >
> > In my experience, not really. We use SPARCs under Solaris 7 and,
> > now, 8. We haven't found any terribly obvious advantages with the
> > system compiled as a 64 bit app, but we _did_ find problems with the
> > 64 bit libraries combined with gcc. As a result of that and
> > pressures to get working on some other things, we stopped testing
> > Postgres as a 64 bit app on Solaris. We haven't done any work on
> > Solaris 8 with it, and that system is a little more mature in the
> > 64-bit-support department, so when I have a chance do to more
> > investigation, I will.
>
> I remember reading in one of the HP guides regarding 64 bit that 64 bit is a
> tool provided for applications. In general no app. should be 64 bit unless
> required. In fact they advice that fastest performance one can get is by
> running 32 bit app. on 64 bit machine because registers are wide and can be
> filled in is less number of fetches.
>
> Sounds reasonable to me.

Dou you, the programmer or SysAdmin, always know when 64 bits is
needed?

Take, for simple example, a memcpy() of 1024 bytes. Most CPUs don't
have direct core-core copy instruction. (The RISC philosophy, after
all, is load-and-store.) A 32-bit executable would need 1024/32 = 32
pairs of load-store operations, while a 64-bit executable would only
need 16. Yes, L1 & L2 caching would help some, but not if you are
moving huge amounts of data...

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