Lexicographically sortable, 128-bit identifier with 48-bit timestamp and 80 random bits. Canonically encoded as a 26 character string, as opposed to the 36 character UUID.

Original implementation and spec: github.com/alizain/ulid

 01an4z07by   79ka1307sr9x4mv3

|----------| |----------------|
 Timestamp       Randomness
  48 bits         80 bits

UUID can be suboptimal for many uses-cases because:

• It isn't the most character efficient way of encoding 128 bits of randomness
• UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
• UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
• UUID v4 provides no other information than randomness, which can cause fragmentation in many data structures

Instead, herein is proposed ULID:

• 128-bit compatibility with UUID
• 1.21e+24 unique ULIDs per millisecond
• Lexicographically sortable
• Canonically encoded as a 26 character string, as opposed to the 36 character UUID
• Uses Douglas Crockford's base 32 for better efficiency and readability (5 bits per character)
• Case insensitive
• No special characters (URL safe)

A simple usage example:

module Main where

import Data.ULID

main :: IO ()
main = do
  -- Derive a ULID using the current time and default random number generator
  ulid1 <- getULID
  print ulid1

  -- Derive a ULID using a specified time and default random number generator
  ulid2 <- getULIDTime 1469918176.385 -- POSIX Time, millisecond precision
  print ulid2

As per the spec, it is also possible to use a cryptographically-secure random number generator to contribute the randomness. However, the programmer must manage the generator on their own.

Example:

module Main where

import Data.ULID

import qualified Crypto.Random       as CR
import qualified Data.ULID.Random    as UR
import qualified Data.ULID.TimeStamp as TS

main :: IO ()
main = do
  -- This default instantiation may not be sufficiently secure.
  -- See the docs at
  -- hackage.haskell.org/package/crypto-api-0.13.2/docs/Crypto-Random.html
  g <- (CR.newGenIO :: IO CR.SystemRandom)

  -- Generate timestamp from current time
  t <- TS.getULIDTimeStamp

  let ulid3 = case UR.mkCryptoULIDRandom g of
          Left err        -> error $ show err
          -- use g2, …, to continue generating secure ULIDs
          Right (rnd, g2) -> ULID t rnd

  print ulid3

stack test

stack bench

Running 1 benchmarks...
Benchmark ulid-bench: RUNNING...
217,868 op/s generate
Benchmark ulid-bench: FINISH