Subject Re: [Firebird-Architect] Digest Number 959
Author Rick Debay
Reverse the order of the elements of a name based UUID:

There is open software out there to generate them.

-----Original Message-----
From: Kevin Berry [mailto:kevinbe71@...]
Sent: Wednesday, March 23, 2005 5:06 PM
Subject: Re: [Firebird-Architect] Digest Number 959

Thanks Ann. Nice theory but....

Here are two serial GUIDs (i.e. produced a split second apart from one
another on my system):


Try to spot the bits they have in common. ;-)

Microsoft started out by making GUIDs serial but....
as the Melissa author discovered... this allowed people to determine
which machine produced the GUIDs.
See reference below (section titled "Algorithm"):

Of course, if you're using some other algorithm that is not the
Microsoft one then I guess this could still hold true. However, I like
to assign a GUID by a system call and using the value in my objects
directly... rather than waiting for the database to assign one and then
having to retrieve it from some output var. This has the added benefit
of objects in memory having unique IDs even if they haven't been stored
in the database yet.


--- "Ann W. Harrison" <aharrison@...> wrote:
> > "reversed GUID" sounds like something you made up?
> A GUID is a string of bytes that is "guaranteed" to be unique. It
> starts with a counter and adds factors that are constant for a
> particular computer. Firebird uses prefix compression on its indexes,

> so having the constant part first reduces the size of indexes by a
> lot.
> Regards,
> Ann

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