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7f4fb34182
It is better developing vmctl tool in VictoriaMetrics repository, so it could be released together with the rest of vmutils tools such as vmalert, vmagent, vmbackup, vmrestore and vmauth.
151 lines
6.6 KiB
Markdown
151 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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