At 02:03 PM 8/29/2002 -0500, Guillermo Najar-Arreola wrote:

>Hi,
>
>I found that GUID is a beautiful candidate for OID; the point is that its a
>string. How much I loose in performance if I use a string primary-key
>instead of a numeric one for ALL my tables ? Of course, if the PK will be
>string, FKs shall be too.

Probably not perceptible, depending on the compression. Different GUID
representations are configured differently. For best compression, put
the least variable part first and the most variable part last. For
example, if the GUID consists of eight bytes of local key, eight bytes
of machine identifier, two bytes of sector of universe, two bytes of
galaxy, four bytes of solar system, two bytes of planet, and four bytes
of manufacturer, you should build the key in this order:

universe, galaxy, solar system, planet, manufacturer, machine, local

The first six sections will be compressed to oblivion, so the average
key length will be about 8 bytes.

The difference in performance between key types has nothing to do with
data type and much to do with average key length.

If you reverse the order, so the key starts with the local value,
the average key length will be something like 30 bytes, so the index
will be nearly 4 times as big.

Regards,

Ann
www.ibphoenix.com
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