Comparison Matrix
| Ver | Input Source | Time Sortable? | Uniqueness | DB Indexing |
|---|---|---|---|---|
| v1 | Time + MAC | No | MAC Address | Terrible |
| v4 | 122 Random Bits | No | Entropy | Poor |
| v7 | Unix Time + Rand | Yes | Time + Entropy | Excellent |
| v3/v5 | Namespace + Name | No | Namespace | Poor |
| v6 | Reordered v1 | Yes | MAC Address | Good |
Why v4 dominates?
It requires zero coordination. You can generate a v4 UUID on an air-gapped toaster and be confident it won't collide with one generated at Google.
Why move to v7?
Database performance. Inserting random v4 UUIDs into a B-Tree index (used by MySQL/Postgres) causes massive fragmentation and I/O overhead. v7 fixes this.
Is v1 dead?
Mostly. Leaking your MAC address is a security risk. v1 is only useful if you absolutely need to know which machine generated a UUID.