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ksuid is a Go library that can generate and parse KSUIDs.


go get -u github.com/segmentio/ksuid

What is a KSUID?

KSUID is for K-Sortable Unique IDentifier. It's a way to generate globally unique IDs similar to RFC 4122 UUIDs, but contain a time component so they can be "roughly" sorted by time of creation. The remainder of the KSUID is randomly generated bytes.

Why use KSUIDs?

Distributed systems often require unique IDs. There are numerous solutions out there for doing this, so why KSUID?

1. Sortable by Timestamp

Unlike the more common choice of UUIDv4, KSUIDs contain a timestamp component that allows them to be roughly sorted by generation time. This is obviously not a strong guarantee as it depends on wall clocks, but is still incredibly useful in practice.

2. No Coordination Required

Snowflake IDs[1] and derivatives require coordination, which significantly increases the complexity of implementation and creates operations overhead. While RFC 4122 UUIDv1s do have a time component, there aren't enough bytes of randomness to provide strong protections against duplicate ID generation.

KSUIDs use 128-bits of pseudorandom data, which provides a 64-times larger number space than the 122-bits in the well-accepted RFC 4122 UUIDv4 standard. The additional timestamp component drives down the extremely rare chance of duplication to the point of near physical infeasibility, even assuming extreme clock skew (> 24-hours) that would cause other severe anomalies.

  1. https://blog.twitter.com/2010/announcing-snowflake

3. Lexographically Sortable, Portable Representations

The binary and string representations are lexicographically sortable, which allows them to be dropped into systems which do not natively support KSUIDs and retain their k-sortable characteristics.

The string representation is that it is base62-encoded, so that they can "fit" anywhere alphanumeric strings are accepted.

How do they work?

KSUIDs are 20-bytes: a 32-bit unsigned integer UTC timestamp and a 128-bit randomly generated payload. The timestamp uses big-endian encoding, to allow lexicographic sorting. The timestamp epoch is adjusted to March 5th, 2014, providing over 100 years of useful life starting at UNIX epoch + 14e8. The payload uses a cryptographically-strong pseudorandom number generator.

The string representation is fixed at 27-characters encoded using a base62 encoding that also sorts lexicographically.

Command Line Tool

This package comes with a simple command-line tool ksuid. This tool can generate KSUIDs as well as inspect the internal components for debugging purposes.

Usage examples

Generate 4 KSUID

$ ./ksuid -n 4

Inspect the components of a KSUID

Using the inspect formatting on just 1 ksuid:

$ ./ksuid -f inspect $(./ksuid)


  String: 0ujtsYcgvSTl8PAuAdqWYSMnLOv
     Raw: 0669F7EFB5A1CD34B5F99D1154FB6853345C9735


       Time: 2017-10-09 21:00:47 -0700 PDT
  Timestamp: 107608047
    Payload: B5A1CD34B5F99D1154FB6853345C9735

Using the template formatting on 4 ksuid:

$ ./ksuid -f template -t '{{ .Time }}: {{ .Payload }}' $(./ksuid -n 4)
2017-10-09 21:05:37 -0700 PDT: 304102BC687E087CC3A811F21D113CCF
2017-10-09 21:05:37 -0700 PDT: EAF0B240A9BFA55E079D887120D962F0
2017-10-09 21:05:37 -0700 PDT: DF0761769909ABB0C7BB9D66F79FC041
2017-10-09 21:05:37 -0700 PDT: 1A8F0E3D0BDEB84A5FAD702876F46543

Generate detailed versions of new KSUID

Generate a new KSUID with the corresponding time using the time formatting:

$ go run cmd/ksuid/main.go -f time -v
0uk0ava2lavfJwMceJOOEFXEDxl: 2017-10-09 21:56:00 -0700 PDT

Generate 4 new KSUID with details using template formatting:

$ ./ksuid -f template -t '{ "timestamp": "{{ .Timestamp }}", "payload": "{{ .Payload }}", "ksuid": "{{.String}}"}' -n 4
{ "timestamp": "107611700", "payload": "9850EEEC191BF4FF26F99315CE43B0C8", "ksuid": "0uk1Hbc9dQ9pxyTqJ93IUrfhdGq"}
{ "timestamp": "107611700", "payload": "CC55072555316F45B8CA2D2979D3ED0A", "ksuid": "0uk1HdCJ6hUZKDgcxhpJwUl5ZEI"}
{ "timestamp": "107611700", "payload": "BA1C205D6177F0992D15EE606AE32238", "ksuid": "0uk1HcdvF0p8C20KtTfdRSB9XIm"}
{ "timestamp": "107611700", "payload": "67517BA309EA62AE7991B27BB6F2FCAC", "ksuid": "0uk1Ha7hGJ1Q9Xbnkt0yZgNwg3g"}

Display the detailed version of a new KSUID:

$ ./ksuid -f inspect


  String: 0ujzPyRiIAffKhBux4PvQdDqMHY
     Raw: 066A029C73FC1AA3B2446246D6E89FCD909E8FE8


       Time: 2017-10-09 21:46:20 -0700 PDT
  Timestamp: 107610780
    Payload: 73FC1AA3B2446246D6E89FCD909E8FE8