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150 lines
6.6 KiB
Markdown
150 lines
6.6 KiB
Markdown
# Universally Unique Lexicographically Sortable Identifier
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[](http://travis-ci.org/oklog/ulid)
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[](https://goreportcard.com/report/oklog/ulid)
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[](https://coveralls.io/github/oklog/ulid?branch=master)
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[](https://godoc.org/github.com/oklog/ulid)
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[](https://raw.githubusercontent.com/oklog/ulid/master/LICENSE)
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A Go port of [alizain/ulid](https://github.com/alizain/ulid) with binary format implemented.
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## Background
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A GUID/UUID can be suboptimal for many use-cases because:
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- It isn't the most character efficient way of encoding 128 bits
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- UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
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- UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
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- UUID v4 provides no other information than randomness which can cause fragmentation in many data structures
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A ULID however:
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- Is compatible with UUID/GUID's
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- 1.21e+24 unique ULIDs per millisecond (1,208,925,819,614,629,174,706,176 to be exact)
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- Lexicographically sortable
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- Canonically encoded as a 26 character string, as opposed to the 36 character UUID
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- Uses Crockford's base32 for better efficiency and readability (5 bits per character)
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- Case insensitive
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- No special characters (URL safe)
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- Monotonic sort order (correctly detects and handles the same millisecond)
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## Install
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```shell
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go get github.com/oklog/ulid
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```
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## Usage
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An ULID is constructed with a `time.Time` and an `io.Reader` entropy source.
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This design allows for greater flexibility in choosing your trade-offs.
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Please note that `rand.Rand` from the `math` package is *not* safe for concurrent use.
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Instantiate one per long living go-routine or use a `sync.Pool` if you want to avoid the potential contention of a locked `rand.Source` as its been frequently observed in the package level functions.
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```go
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func ExampleULID() {
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t := time.Unix(1000000, 0)
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entropy := ulid.Monotonic(rand.New(rand.NewSource(t.UnixNano())), 0)
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fmt.Println(ulid.MustNew(ulid.Timestamp(t), entropy))
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// Output: 0000XSNJG0MQJHBF4QX1EFD6Y3
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}
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```
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## Specification
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Below is the current specification of ULID as implemented in this repository.
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### Components
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**Timestamp**
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- 48 bits
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- UNIX-time in milliseconds
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- Won't run out of space till the year 10895 AD
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**Entropy**
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- 80 bits
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- User defined entropy source.
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- Monotonicity within the same millisecond with [`ulid.Monotonic`](https://godoc.org/github.com/oklog/ulid#Monotonic)
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### Encoding
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[Crockford's Base32](http://www.crockford.com/wrmg/base32.html) is used as shown.
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This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.
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```
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0123456789ABCDEFGHJKMNPQRSTVWXYZ
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```
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### Binary Layout and Byte Order
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The components are encoded as 16 octets. Each component is encoded with the Most Significant Byte first (network byte order).
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```
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 32_bit_uint_time_high |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 16_bit_uint_time_low | 16_bit_uint_random |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 32_bit_uint_random |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 32_bit_uint_random |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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```
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### String Representation
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```
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01AN4Z07BY 79KA1307SR9X4MV3
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|----------| |----------------|
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Timestamp Entropy
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10 chars 16 chars
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48bits 80bits
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base32 base32
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```
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## Test
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```shell
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go test ./...
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```
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## Benchmarks
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On a Intel Core i7 Ivy Bridge 2.7 GHz, MacOS 10.12.1 and Go 1.8.0beta1
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```
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BenchmarkNew/WithCryptoEntropy-8 2000000 771 ns/op 20.73 MB/s 16 B/op 1 allocs/op
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BenchmarkNew/WithEntropy-8 20000000 65.8 ns/op 243.01 MB/s 16 B/op 1 allocs/op
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BenchmarkNew/WithoutEntropy-8 50000000 30.0 ns/op 534.06 MB/s 16 B/op 1 allocs/op
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BenchmarkMustNew/WithCryptoEntropy-8 2000000 781 ns/op 20.48 MB/s 16 B/op 1 allocs/op
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BenchmarkMustNew/WithEntropy-8 20000000 70.0 ns/op 228.51 MB/s 16 B/op 1 allocs/op
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BenchmarkMustNew/WithoutEntropy-8 50000000 34.6 ns/op 462.98 MB/s 16 B/op 1 allocs/op
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BenchmarkParse-8 50000000 30.0 ns/op 866.16 MB/s 0 B/op 0 allocs/op
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BenchmarkMustParse-8 50000000 35.2 ns/op 738.94 MB/s 0 B/op 0 allocs/op
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BenchmarkString-8 20000000 64.9 ns/op 246.40 MB/s 32 B/op 1 allocs/op
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BenchmarkMarshal/Text-8 20000000 55.8 ns/op 286.84 MB/s 32 B/op 1 allocs/op
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BenchmarkMarshal/TextTo-8 100000000 22.4 ns/op 714.91 MB/s 0 B/op 0 allocs/op
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BenchmarkMarshal/Binary-8 300000000 4.02 ns/op 3981.77 MB/s 0 B/op 0 allocs/op
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BenchmarkMarshal/BinaryTo-8 2000000000 1.18 ns/op 13551.75 MB/s 0 B/op 0 allocs/op
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BenchmarkUnmarshal/Text-8 100000000 20.5 ns/op 1265.27 MB/s 0 B/op 0 allocs/op
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BenchmarkUnmarshal/Binary-8 300000000 4.94 ns/op 3240.01 MB/s 0 B/op 0 allocs/op
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BenchmarkNow-8 100000000 15.1 ns/op 528.09 MB/s 0 B/op 0 allocs/op
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BenchmarkTimestamp-8 2000000000 0.29 ns/op 27271.59 MB/s 0 B/op 0 allocs/op
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BenchmarkTime-8 2000000000 0.58 ns/op 13717.80 MB/s 0 B/op 0 allocs/op
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BenchmarkSetTime-8 2000000000 0.89 ns/op 9023.95 MB/s 0 B/op 0 allocs/op
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BenchmarkEntropy-8 200000000 7.62 ns/op 1311.66 MB/s 0 B/op 0 allocs/op
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BenchmarkSetEntropy-8 2000000000 0.88 ns/op 11376.54 MB/s 0 B/op 0 allocs/op
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BenchmarkCompare-8 200000000 7.34 ns/op 4359.23 MB/s 0 B/op 0 allocs/op
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```
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## Prior Art
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- [alizain/ulid](https://github.com/alizain/ulid)
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- [RobThree/NUlid](https://github.com/RobThree/NUlid)
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- [imdario/go-ulid](https://github.com/imdario/go-ulid)
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