1# Globally Unique ID Generator
2
3[](https://godoc.org/github.com/rs/xid) [](https://raw.githubusercontent.com/rs/xid/master/LICENSE) [](https://travis-ci.org/rs/xid) [](http://gocover.io/github.com/rs/xid)
4
5Package xid is a globally unique id generator library, ready to safely be used directly in your server code.
6
7Xid uses the Mongo Object ID algorithm to generate globally unique ids with a different serialization (base64) to make it shorter when transported as a string:
8https://docs.mongodb.org/manual/reference/object-id/
9
10- 4-byte value representing the seconds since the Unix epoch,
11- 3-byte machine identifier,
12- 2-byte process id, and
13- 3-byte counter, starting with a random value.
14
15The binary representation of the id is compatible with Mongo 12 bytes Object IDs.
16The string representation is using base32 hex (w/o padding) for better space efficiency
17when stored in that form (20 bytes). The hex variant of base32 is used to retain the
18sortable property of the id.
19
20Xid doesn't use base64 because case sensitivity and the 2 non alphanum chars may be an
21issue when transported as a string between various systems. Base36 wasn't retained either
22because 1/ it's not standard 2/ the resulting size is not predictable (not bit aligned)
23and 3/ it would not remain sortable. To validate a base32 `xid`, expect a 20 chars long,
24all lowercase sequence of `a` to `v` letters and `0` to `9` numbers (`[0-9a-v]{20}`).
25
26UUIDs are 16 bytes (128 bits) and 36 chars as string representation. Twitter Snowflake
27ids are 8 bytes (64 bits) but require machine/data-center configuration and/or central
28generator servers. xid stands in between with 12 bytes (96 bits) and a more compact
29URL-safe string representation (20 chars). No configuration or central generator server
30is required so it can be used directly in server's code.
31
32| Name | Binary Size | String Size | Features
33|-------------|-------------|----------------|----------------
34| [UUID] | 16 bytes | 36 chars | configuration free, not sortable
35| [shortuuid] | 16 bytes | 22 chars | configuration free, not sortable
36| [Snowflake] | 8 bytes | up to 20 chars | needs machine/DC configuration, needs central server, sortable
37| [MongoID] | 12 bytes | 24 chars | configuration free, sortable
38| xid | 12 bytes | 20 chars | configuration free, sortable
39
40[UUID]: https://en.wikipedia.org/wiki/Universally_unique_identifier
41[shortuuid]: https://github.com/stochastic-technologies/shortuuid
42[Snowflake]: https://blog.twitter.com/2010/announcing-snowflake
43[MongoID]: https://docs.mongodb.org/manual/reference/object-id/
44
45Features:
46
47- Size: 12 bytes (96 bits), smaller than UUID, larger than snowflake
48- Base32 hex encoded by default (20 chars when transported as printable string, still sortable)
49- Non configured, you don't need set a unique machine and/or data center id
50- K-ordered
51- Embedded time with 1 second precision
52- Unicity guaranteed for 16,777,216 (24 bits) unique ids per second and per host/process
53- Lock-free (i.e.: unlike UUIDv1 and v2)
54
55Best used with [zerolog](https://github.com/rs/zerolog)'s
56[RequestIDHandler](https://godoc.org/github.com/rs/zerolog/hlog#RequestIDHandler).
57
58Notes:
59
60- Xid is dependent on the system time, a monotonic counter and so is not cryptographically secure. If unpredictability of IDs is important, you should not use Xids. It is worth noting that most other UUID-like implementations are also not cryptographically secure. You should use libraries that rely on cryptographically secure sources (like /dev/urandom on unix, crypto/rand in golang), if you want a truly random ID generator.
61
62References:
63
64- http://www.slideshare.net/davegardnerisme/unique-id-generation-in-distributed-systems
65- https://en.wikipedia.org/wiki/Universally_unique_identifier
66- https://blog.twitter.com/2010/announcing-snowflake
67- Python port by [Graham Abbott](https://github.com/graham): https://github.com/graham/python_xid
68- Scala port by [Egor Kolotaev](https://github.com/kolotaev): https://github.com/kolotaev/ride
69- Rust port by [Jérôme Renard](https://github.com/jeromer/): https://github.com/jeromer/libxid
70- Ruby port by [Valar](https://github.com/valarpirai/): https://github.com/valarpirai/ruby_xid
71- Java port by [0xShamil](https://github.com/0xShamil/): https://github.com/0xShamil/java-xid
72- Dart port by [Peter Bwire](https://github.com/pitabwire): https://pub.dev/packages/xid
73
74## Install
75
76 go get github.com/rs/xid
77
78## Usage
79
80```go
81guid := xid.New()
82
83println(guid.String())
84// Output: 9m4e2mr0ui3e8a215n4g
85```
86
87Get `xid` embedded info:
88
89```go
90guid.Machine()
91guid.Pid()
92guid.Time()
93guid.Counter()
94```
95
96## Benchmark
97
98Benchmark against Go [Maxim Bublis](https://github.com/satori)'s [UUID](https://github.com/satori/go.uuid).
99
100```
101BenchmarkXID 20000000 91.1 ns/op 32 B/op 1 allocs/op
102BenchmarkXID-2 20000000 55.9 ns/op 32 B/op 1 allocs/op
103BenchmarkXID-4 50000000 32.3 ns/op 32 B/op 1 allocs/op
104BenchmarkUUIDv1 10000000 204 ns/op 48 B/op 1 allocs/op
105BenchmarkUUIDv1-2 10000000 160 ns/op 48 B/op 1 allocs/op
106BenchmarkUUIDv1-4 10000000 195 ns/op 48 B/op 1 allocs/op
107BenchmarkUUIDv4 1000000 1503 ns/op 64 B/op 2 allocs/op
108BenchmarkUUIDv4-2 1000000 1427 ns/op 64 B/op 2 allocs/op
109BenchmarkUUIDv4-4 1000000 1452 ns/op 64 B/op 2 allocs/op
110```
111
112Note: UUIDv1 requires a global lock, hence the performance degradation as we add more CPUs.
113
114## Licenses
115
116All source code is licensed under the [MIT License](https://raw.github.com/rs/xid/master/LICENSE).
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