Re: UUID column as pimrary key?

On Wed, Jan 5, 2011 at 1:03 PM, Bill Moran <wmoran(at)potentialtech(dot)com> wrote:
>
> But the point (that you are trying to sidestep) is that the UUID namespace
> is finite, so therefore you WILL hit a problem with conflicts at some point.
> Just because that point is larger than most people have to concern themselves
> with isn't an invalidation.

The UUID itself is 128 bits. Some of those bits are pre-determined.
I don't recall, but I think that a "normal" UUID has 121 bits of
randomness.

How many would one have to store in a database before a collision
would even be a concern. Such a database would be freaking huge.
Probably far larger than anything that anyone has.

Lets say (I'm pulling numbers out of my ass here), that you wanted to
store 2^100 rows in a table. Each row would have a UUID and some
other meaningful data. Maybe a short string or something. I don't
recall what the postgresql row overhead is (~20 bytes?), but lets say
that each row in your magic table of death required 64 bytes. A table
with 2^100 rows would require nearly 10^31 bytes ( = log_10(64 *
2^100)). How on Earth would you store that much data? And why would
you ever need to?

I postulate that UUID collisions in Postgresql, using a "good" source
for UUID generation, is unlikely to have collisions for any reasonable
database.

Food for thought:
http://blogs.sun.com/dcb/entry/zfs_boils_the_ocean_consumes

ps- If my math is off, I apologize. Its been a long day...