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Having witnessed a uuid collision in only millions records, I can assure you it's not a laughing matter.

That is likely due to a fault in the UUID generator, rather than the concept of using UUIDs.

http://www.h2database.com/html/advanced.html#uuid

Well than the java implementation of UUID is flawed!

You say 'only millions records'. Even if you had 2^36 records (that's over 68 billion) the chances of a collision should be 0.0000000000000004

That really is vanishingly small.

So, rationally, I'd guess it is more likely there is a problem with the implementation of UUID you are using, or just perhaps there is some other cause of the collision...like a bug?

Also possibly a problem with the version of UUID used. A v1 UUID is somewhat likely to collide if machines share MAC addresses and/or have problematic clocks.

The likelihood of a v4 collision is tied to the strength of the platform's (crypto) RNG.

If the UUIDs are actually being picked uniformly, the fear is entirely irrational, I agree. However, fear that the distribution isn't actually uniform in real implementations is much less crazy.

lol