uuid types 3 and 5

[Monte Goulding]

On 10/01/2014, at 9:22 AM, Martin Baxter wrote:

> So I take it that the situations where you would use this type of uuid
> are really similar to those situations where you might use a hash, but
> where a simple hash wouldn't povide a high enough probability of
> uniqueness for the context.

Actually a sha1 hash is more likely to be unique than a uuid. I really don't see the advantage of using type 3 or 5 uuid rather than sha1 as in:
local tSHA
get binaryDecode("h*",sha1Digest("hello"), tSHA)
answer tSHA

Other than saving a few bits because the uuid is shorter... and perhaps that you can do things like upgrade from md5 based to sha based without messing with your database. Type 3 and 5 uuids are basically most bits form the hash and some other bits to identify the type.

I suspect git would be the most heavily used distributed database in use and it's built on the sha 1 hash. Even in the biggest git repo (the linux kernel) they only need to use the first 12 chars of the sha to uniquely identify the object in the database.

Cheers

--
M E R Goulding 
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