On Tue, Nov 04, 2014 at 08:30:21AM +0000, Laurenz Albe wrote:
> David Fetter wrote:
> > On Tue, Nov 04, 2014 at 07:51:06AM +0900, Tatsuo Ishii wrote:
> >> Just out of curiosity, why is Oracle's NUMBER (I assume you are
> >> talking about this) so fast?
> >
> > I suspect that what happens is that NUMBER is stored as a native
> > type (int2, int4, int8, int16) that depends on its size and then
> > cast to the next upward thing as needed, taking any performance
> > hits at that point. The documentation hints (38 decimal places)
> > at a 128-bit internal representation as the maximum. I don't know
> > what happens when you get past what 128 bits can represent.
>
> No, Oracle stores NUMBERs as variable length field (up to 22 bytes),
> where the first byte encodes the sign and the comma position and the
> remaining bytes encode the digits, each byte representing two digits
> in base-100 notation (see Oracle Metalink note 1007641.6).
Thanks for clearing that up, and sorry for spreading misinformed
guesses.
> So it's not so different from PostgreSQL.
> No idea why their arithmetic should be faster.
I have an idea, but this time, I think it's right. They have at least
one team of people whose job it is to make sure that it is fast.
Cheers,
David.
--
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