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1.6. UUIDv6

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Fabio Lima edited this page Sep 25, 2022 · 3 revisions

Time-ordered UUID

It is one of the UUID formats proposed in an IETF draft.

The Time-ordered UUID has a timestamp and a node identifier. These two information represent WHEN and WHERE the UUID was created.

The timestamp is the count of 100 nanosecond intervals since 1582-10-15, the beginning of Gregorian calendar.

The timestamp bytes are kept in the original order, unlike the time-based UUID (version 1). This is the only difference between version 1 and version 6.

The node identifier can be a MAC address, a hash of system information, a specific number or a random number (default).

See the section Choosing the node identifier.

// with a static random number as node identifier
UUID uuid = UuidCreator.getTimeOrdered();
// with a MAC address as node identifier
UUID uuid = UuidCreator.getTimeOrderedWithMac();
// with a hash of hostname, MAC and IP as node identifier
UUID uuid = UuidCreator.getTimeOrderedWithHash();
// with a changing random number as node identifier
UUID uuid = UuidCreator.getTimeOrderedWithRandom();

Sequence of time-ordered UUIDs:

1e98eff0-eddc-6470-a649-ad1cde652e10
1e98eff0-eddc-6471-a649-ad1cde652e10
1e98eff0-eddc-6472-a649-ad1cde652e10
1e98eff0-eddc-6473-a649-ad1cde652e10
1e98eff0-eddc-6474-a649-ad1cde652e10
1e98eff0-eddc-6475-a649-ad1cde652e10
1e98eff0-eddc-6476-a649-ad1cde652e10
1e98eff0-eddc-6477-a649-ad1cde652e10
1e98eff0-eddc-6478-a649-ad1cde652e10
1e98eff0-eddc-6479-a649-ad1cde652e10
1e98eff0-eddc-647a-a649-ad1cde652e10
1e98eff0-eddc-647b-a649-ad1cde652e10
1e98eff0-eddc-647c-a649-ad1cde652e10
1e98eff0-eddc-647d-a649-ad1cde652e10
1e98eff0-eddc-647e-a649-ad1cde652e10
1e98eff0-eddc-647f-a649-ad1cde652e10
                 ^ look

|-----------------|----|-----------|
     timestamp    clkseq  node id

Other usage examples:

// Time-ordered with a date and time chosen by you
Instant myInstant = Instant.parse("1987-01-23T01:23:45.123456789Z");
UUID uuid = UuidCreator.getTimeOrdered(myInstant, null, null);
// Time-ordered with a clock sequence chosen by you
Integer myClockSeq = 0xAAAA; // Override the random clock sequence
UUID uuid = UuidCreator.getTimeOrdered(null, myClockSeq, null);
// Time-ordered with a node identifier chosen by you
Long myNode = 0xAAAAAAAAAAAAL; // Override the random node identifier
UUID uuid = UuidCreator.getTimeOrdered(null, null, myNode);

Implementation

Time-ordered and Time-based UUID share the same base implementation and examples. This section will focus on the only difference between them.

The Time-ordered UUID inherits the same characteristics of the time-based UUID. The only difference is that the timestamp bits are not rearranged as the Time-based UUID does.

Time-ordered timestamp arrangement
 00000000-0000-v000-m000-000000000000
|1-------|2---|3---|
1: timestamp high   *****
2: timestamp mid     ***
3: timestamp low      *

Time-based vs Time-ordered

The RFC-4122 splits the timestamp bits into three parts: high, middle, and low. Then it reverses the order of these three parts to create a time-based UUID. The reason for this layout is not documented in the RFC-4122.

In the time-ordered, the timestamp bits are kept in the original layout. See the comparison below.

Instant:

 2019-09-22T17:52:55.033Z

Instant's timestamp in hexadecimal:

 01e9dd61ce117e90

Timestamp split into high, middle and low bits:

 _1e9 dd61 ce117e90
 _aaa bbbb cccccccc

a: time high
b: time middle
c: time low
_: version

Timestamp in time-based layout (version 1):

 ce117e90-dd61-11e9-0000-000000000000
 cccccccc-bbbb-_aaa-dddd-eeeeeeeeeeee

c: time low
b: time middle
a: time high
_: version
d: clock sequence
e: node id

Timestamp in time-ordered layout (version 6):

 1e9dd61c-e117-6e90-0000-000000000000
 aaabbbbc-cccc-_ccc-dddd-eeeeeeeeeeee

a: time high
b: time middle
c: time low
_: version
d: clock sequence
e: node id
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