Universally Unique Lexicographically Sortable Identifier

A Clojure port of alizain/ulid

Background

A GUID/UUID can be suboptimal for many use-cases because:

• It isn't the most character efficient way of encoding 128 bits
• It provides no other information than randomness

A ULID however:

• Is compatible with UUID/GUID's
• 1.21e+24 unique ULIDs per millisecond (1,208,925,819,614,629,174,706,176 to be exact)
• Lexicographically sortable
• Canonically encoded as a 26 character string, as opposed to the 36 character UUID
• Uses Crockford's base32 for better efficiency and readability (5 bits per character)
• Case insensitive
• No special characters (URL safe)

Usage

Generating a ULID String requires a ULID instance.

(require '[clj-ulid :as ulid])


; Generate ULID
(ulid/ulid)
; => "01bpf8bvjp4qas6vkg9maa13b5"

; Generate ULID from timestamp (useful for migrations)
(ulid/ulid 1501602817887)
; => "01bpf819tzbqdgxryyf664y7vs"

; Get embedded timestamp from ULID
(ulid/ulid->timestamp "01bpf819tzbqdgxryyf664y7vs")
; => 1501602817887

Specification

Below is the current specification of ULID as implemented in this repository.

Components

Timestamp

• 48 bits
• UNIX-time in milliseconds
• Won't run out of space till the year 10889 AD

Entropy

• 80 bits
• User defined entropy source.

Encoding

Crockford's Base32 is used as shown. This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.

0123456789ABCDEFGHJKMNPQRSTVWXYZ

String Representation

 01AN4Z07BY      79KA1307SR9X4MV3
|----------|    |----------------|
 Timestamp           Entropy
  10 chars           16 chars
   48bits             80bits
   base32             base32

Test

lein test

Prior Art

• alizain/ulid