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Re: Patch for UUID datatype (beta)

From: "Harald Armin Massa" <haraldarminmassa(at)gmail(dot)com>
To: "Gevik Babakhani" <pgdev(at)xs4all(dot)nl>
Cc: "Andreas Pflug" <pgadmin(at)pse-consulting(dot)de>, pgsql-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Patch for UUID datatype (beta)
Date: 2006-09-18 09:11:04
Message-ID: 7be3f35d0609180211p752e4662u3373d988d984ffa5@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Gevik,
>uniqueness is never a guaranteed. that is according to the RFC docs.

>uniqueness is never a guaranteed in the sense that there is a tiny
>chance someone of the other side of the planet might generate the same
>guid.

As much as I learned, it is recommended to give information about "grade of
uniqueness". I think it would be a valuable information, which information
your UUID-generator takes into account, and what the "grade of uniqueness"
is.

(I know of the Windows UUID, which takes the MAC-Address of the included
Ethernet-Card into it's calculation, which may be guaranteed to be unique)


Some more questions about UUIDs and your patch:

a) compatibility of UUIDs   -> I have generated a lot of UUIDs via the WIN32
provided function (for the unix-only-people: Windows uses UUIDs all around
its registry, software IDs and on and on). How unique are those UUIDs when
mixed with "your" UUIDs ?

b) I read some time ago about the problems with UUIDs as primary keys in
contrast to serials: serials get produced in ascending order; and often data
which was produced in one timespan is also connected semantically. "near
serial values" are also local within a btree-index; but UUIDs generated in
"near times" are usually spread around the possible bitranges.
(example for sequence of serials: 1 - 2 - 3 - 4 - 5 - 6
 example for sequence of UUIDs : 1 - 999919281921843191 - 782 -
18291831912318971231)
that is supposed to affect the locality of the index, and from that also the
performance of the system.

I do not know how valid this information is; so I am asking you for your
feedback; especially since you put a lot of thoughts into this UUID patch.
Maybe you took allready care of this situation when constructing the index
operators?

Thanks

Harald






-- 
GHUM Harald Massa
persuadere et programmare
Harald Armin Massa
Reinsburgstra├če 202b
70197 Stuttgart
0173/9409607
-
Let's set so double the killer delete select all.

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