ulid4j

ulid4j is a java library for generating stupidly fast ULID (in less than 100ns).

Design

A ULID is composed of two parts:

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

• The first 48 bits represents the amount of milliseconds since Unix Epoch, 1 January 1970.

• The next 80 bits represent randomness and are generated using a secure random generator. However, instead of using java's Random or SecureRandom to generate the random bits, ulid4j uses a fast-key-erasure CSPRNG, implemented through a SipHash-2-4, to generate two random numbers. Since SipHash is a cryptographically strong PRF, the generated random numbers would be uniformly distributed.

When generating ULID, if the same millisecond is detected, the LSB of random part is simply incremented by 1 bit. However, once the millisecond changes, the random part is reset to a new value.

Benchmark

This section shows benchmarks comparing ulid4j to sulky-ulid, ulid-creator and java.util.UUID.

System:

• JDK 1.8.0_272
• Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz
• Ubuntu 20.04

--------------------------------------------------------------------
THROUGHPUT            Mode    Cnt        Score       Error  Units
--------------------------------------------------------------------
ulid_creator          thrpt    5   4701028.527 ± 30450.135  ops/s
sulky_ulid            thrpt    5   1264087.411 ± 23769.113  ops/s
java_UUID             thrpt    5   1275500.236 ± 27089.688  ops/s
ulid4j                thrpt    5  13905799.018 ± 60290.838  ops/s
--------------------------------------------------------------------

--------------------------------------------------------------------
AVERAGE TIME          Mode   Cnt     Score    Error  Units
--------------------------------------------------------------------
ulid_creator          avgt    5    213.341 ±  1.964  ns/op
sulky_ulid            avgt    5    790.365 ±  2.956  ns/op
java_UUID             avgt    5    796.800 ±  5.221  ns/op
ulid4j                avgt    5     71.991 ±  0.423  ns/op
--------------------------------------------------------------------

Installation

Gradle

    dependencies {
        implementation 'dev.shamil:ulid4j:1.0'
    }

Maven

    <dependency>
      <groupId>dev.shamil</groupId>
      <artifactId>ulid4j</artifactId>
      <version>1.0</version>
    </dependency>

Usage

Before generating ULID string, a ulid4j.Ulid() instance needs to be created.

    import ulid4j.Ulid;

    Ulid ulidGenerator = new Ulid();

This creates a java.security.SecureRandom underneath, however Ulid(SecureRandom) constructor can be used to provide a custom implementation as well. This SecureRandom is used to generate the initial SipHash states.

Once the Ulid instance gets created, the same should be used to generate multiple ULIDs (preferably until the JVM shutdowns).

• Get monotonically increasing ULID:

      String ulid = ulidGenerator.next();

  Sequence of ULIDs that will be generated:

      timestamp   randomness
      |--------|---------------|
      01ENPZEF91HVP9WHSVE88GX8TD
      01ENPZEF91HVP9WHSVE88GX8TE
      01ENPZEF91HVP9WHSVE88GX8TF
      01ENPZEF91HVP9WHSVE88GX8TG
      01ENPZEF91HVP9WHSVE88GX8TH
      01ENPZEF91HVP9WHSVE88GX8TJ
      01ENPZEF91HVP9WHSVE88GX8TK
      01ENPZEF91HVP9WHSVE88GX8TM
      01ENPZEF91HVP9WHSVE88GX8TN
      01ENPZEF91HVP9WHSVE88GX8TP
      01ENPZEF91HVP9WHSVE88GX8TQ
      01ENPZEF91HVP9WHSVE88GX8TR
      01ENPZEF92FB0DCK7MVE8780NE  <-- millisecond changed
      01ENPZEF92FB0DCK7MVE8780NF
      01ENPZEF92FB0DCK7MVE8780NG
      01ENPZEF92FB0DCK7MVE8780NH
      01ENPZEF92FB0DCK7MVE8780NJ
      01ENPZEF92FB0DCK7MVE8780NK
      01ENPZEF92FB0DCK7MVE8780NM
      01ENPZEF92FB0DCK7MVE8780NN
      01ENPZEF92FB0DCK7MVE8780NP
      01ENPZEF92FB0DCK7MVE8780NQ
  

• Get a random ULID (monotonicity is not a requirement):

      String ulid = ulidGenerator.create(); // 01ENPZEF91HVP9WHSVE88GX8TE

Ulid also contains static methods to

• check if a String is a valid Ulid

    String str1 = "01ENPZEF91HVP9WHSVE88GX8TE";
    String str2 = "0e144db1e46f442da30bcf6e31a20ca8";
    
    Ulid.isValid(str1); // true
    Ulid.isValid(str2); // false

• extract the unix time from a Ulid string

    String ulidStr = ulidGenerator.next(); // 01ENQGX8XAF941RDPKPXSQQH4Z
    long unixTime = Ulid.unixTime(ulidStr);  // 1603886031786

License

The source code is licensed under the MIT License.