Overview
- UUIDv1 - UUIDv5: in RFC4122
- Others: RFC 9562
- 128 bits in size
- Big endian
Fields
Variant Field
- Determines the layout of the UUID
- Could be called type field
- consists of a variable number of the most significant bits of octet 8 of the UUID.
UUIDv1
- Time Based UUID
- Starting Time: Oct 15, 1568 (Gregorian Calendar) UTC
- Clock sequence: avoid dups that arise when clock is set backwards in time
- when time and node changes, it + 1 and mod 214
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_low |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_mid | ver | time_high |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var| clock_seq | node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Problmes:
- uncommon 100-nanosecond Gregorian Epoch (compared to Unix Timestamp)
- timestamp is hard to be represented in ieee 754
- Not time ordered, bad locality for B Tree
Tricks
- Store in binary to save space and faster comparison on time
Links