Re: New to PostgreSQL, performance considerations

On Mon, Dec 11, 2006 at 11:09:13AM -0200, Daniel van Ham Colchete wrote:
>> You know what? I don't.
> So test it yourself.

You're making the claims, you're supposed to be proving them...

> As I said, it is an example. Take floatpoint divisions. You have
> plenty of ways of doing it: 387, MMX, SSE, 3dNow, etc... Here GCC have
> to make a choice.

No, you don't. MMX, SSE and 3Dnow! will all give you the wrong result
(reduced precision). SSE2, on the other hand, has double precision floats, so
you might have a choice there -- except that PostgreSQL doesn't really do a
lot of floating-point anyhow.

> And this is only one case. Usually, compiler optimizations are really
> complex and the processor's timings counts a lot.

You keep asserting this, with no good backing.

> If you still can't imagine any case, you can read Intel's assembler
> reference. You'll see that there are a lot of ways of doing a lot of
> things.

I've been programming x86 assembler for ten years or so...

> Steinar, you should really test it. I won't read the PostgreSQL source
> to point you were it could use SSE or SSE2 or whatever. And I won't
> read glibc's code.

Then you should stop making these sort of wild claims.

> You don't need to belive in what I'm saying. You can read GCC docs,
> Intel's assembler reference, AMD's docs about their processor and
> about how diferent that arch is.

I have.

/* Steinar */
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