CHash is a yet another consistent hashing library in Clojure, heavily inspired by the implementation in Riak Core.

CHash is not a young project and based on the consistent hashing implementation from Riak Core which is mature.

CHash artifacts are released to Clojars. If you are using Maven, add the following repository definition to your pom.xml:

<repository>
  <id>clojars.org</id>
  <url>http://clojars.org/repo</url>
</repository>

With Leiningen:

[clojurewerkz/chash "1.1.0"]

With Maven:

<dependency>
  <groupId>clojurewerkz</groupId>
  <artifactId>chash</artifactId>
  <version>1.1.0</version>
</dependency>

CHash is a very small library so there are no documentation guides.

(require '[clojurewerkz.chash.ring :as ch])

;; create a new ring with 64 partitions and a seed node (value)
(ch/fresh 64 "seed")

;; update a partition
(let [r (ch/fresh 64 "seed")]
  (ch/update r 0 "node2"))

;; retrieve 3 partitions in order starting at the given point on the ring
(let [r (ch/fresh 64 "seed")]
  (ch/successors r (ch/key-of 0) 3))

;; check if a particular node claims any partitions in the ring
(let [r (ch/fresh 64 "seed")]
  (ch/claimant? r "node2"))

;; given a key as an integer, get the next ring partition
(let [r (ch/fresh 64 "seed")]
  (ch/next-index r (ch/key-of 128)))

;; randomized merging of two rings. When two nodes claim the same partition,
;; the owner in the resulting ring is selected randomly
(let [r1 (ch/fresh 64 "node1")
      r2 (ch/fresh 64 "node2")]
  (ch/merge r1 r2))

See documentation strings for clojurewerkz.chash.core functions and our test suite.

CHash requires Clojure 1.4 or later.

CHash is part of the group of Clojure libraries known as ClojureWerkz, together with Monger, Welle, Langohr, Elastisch, Neocons and several others.

CHash uses Leiningen 2. Make sure you have it installed and then run tests against supported Clojure versions using

lein all test

Then create a branch and make your changes on it. Once you are done with your changes and all tests pass, submit a pull request on Github.

Copyright (C) 2012-2016 Michael S. Klishin, Alex Petrov, and the ClojureWerkz team.

Double licensed under the Eclipse Public License (the same as Clojure) or the Apache Public License 2.0.