Irmin is a library for persistent stores with built-in snapshot,
branching and reverting mechanisms. It is designed to use a large
variety of backends. Irmin is written in pure OCaml and does not
depend on external C stubs; it aims to run everywhere, from Linux,
to browsers and Xen unikernels.

Description

Irmin is a library to version-control application data. It has the following
features:

• on-disk format various formats are supported, including the Git format:
  Irmin on-disk repositories can be inspected and modified using the classic
  Git command-line tools.

• wire format various formats are supported, including the Git protocol
  (only in client mode) or a simple JSON-based REST API (client and server).

• dynamic behaviour Irmin allows the users to define custom merge functions,
  to use in-memory transactions (to keep track of reads as well as writes) and
  to define event-driven workflows using a notification mechanism.

These abstractions allow developers to create applications with concurrent
behaviors which are both efficient and safe.

Bindings to other languages

• Go irmin-go

• JavaScript irmin-js

Backends

Irmin ships with various backends. It provides the following OCamlfind pacakges:

• irmin.mem is an in-memory backend.

• irmin.git uses the Git format to persist data on disk.

• irmin.fs uses bin_prot to persist
  data on disk.

• irmin.http uses JSON over HTTP to speak with an Irmin server.

Other external backends are available as external OPAM packages
(use opam install <pkg> to install):

• irmin-chunk stores raw contents into
  a well-balanced rope where leafs are chunks of all the same size.

• irmin-indexdb is a backend
  for a web browser's IndexedDB store.

Datastructures

• merge-queues is an implementation
  of mergeable queues.

• merge-ropes is an implementation
  of mergeable ropes.

• diff-datatypes is a collection
  of automatic merge functions based on edit scripts. It is fairly generic but
  contains specific implementation for mergeable trees, stacks and queues.

• irmin-datatypes is a
  collection of mergeable datatypes, including LWW registers, queues and sets.

Use-Cases

Here a list of Irmin users:

• Cuekeeper a
  version-controlled TODO list in the browser.

• imaplet, a version-controlled
  IMAP server and client.

• jitsu, a DNS server that automatically
  starts unikernels on demand. The database is persisted with Irmin.

• Irmin+Xenstore, the
  Xenstore deamon rewritten to use Irmin to persist its data.

• irmin-arp, a distributed ARP cache.

• dog, a synchronisation tool.

• irminFS, a prototype version-controlled
  file-system using Fuse.

Further Reading

• What a Distributed, Version-Controlled ARP Cache Gets
  You.
  Blog post describing how Irmin can be used with Mirage to store the
  network stack's ARP cache, which allows the history to be viewed using
  the git tools.

• CueKeeper: Gitting Things Done in the
  Browser.
  A GTD-based todo list running client-side in the browser, using Irmin
  compiled to JavaScript to provide history, revert and synchronisation
  between tabs. The data is stored using an IndexedDB Irmin backend.

• Using Irmin to add fault-tolerance to the Xenstore
  database.
  Porting the Xen hypervisor toolstack to support Git persistence via
  Irmin.

• Introducing Irmin: Git-like distributed, branchable
  storage. This is the first
  post that describes Irmin, the new Git-like storage layer for Mirage
  OS 2.0.

Getting Started

Install

Irmin is packaged with opam:

opam install irmin-unix # install all the optional depencies

Usage

Irmin comes with a command-line tool called irmin. See irmin --help for further reading. Use either irmin <command> --help or
irmin help <command> for more information on a specific command.

To get the full capabilites of Irmin, use the API:

open Lwt.Infix
open Irmin_unix
module Store = Irmin_unix.Git.FS.KV (Irmin.Contents.String)

let config = Irmin_git.config ~bare:true "/tmp/irmin/test"
let info fmt = Irmin_unix.info ~author:"me <me@moi.com>" fmt

let prog =
  Store.Repo.v config >>= Store.master >>= fun t ->
  Store.set t ~info:(info "Updating foo/bar") ["foo"; "bar"] "hi!" >>= fun () ->
  Store.get t ["foo"; "bar"] >>= fun x ->
  Printf.printf "Read: %s\n%!" x;
  Lwt.return_unit

let () = Lwt_main.run prog

To compile the example above, save it to a file called
example.ml. Install irmin and git with opam (opam install irmin-unix) and
run

$ ocamlfind ocamlopt example.ml -o example -package irmin.unix,lwt.unix -linkpkg
$ ./example
Read: hi!

The examples directory contains more examples. To build them, run

$ ./configure --enable-examples
$ make

Tutorial

Tutorials are available on the
wiki.

Issues

To report any issues please use the bugtracker on
Github.

Conditions

See the LICENSE file.

Acknowledgements

Development of Irmin was supported in part by the EU FP7 User-Centric Networking
project, Grant No. 611001.