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Irmin is a distributed database that follows the same design principles as Git
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Irmin - A distributed database built on the same principles as Git

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Irmin is an OCaml library for building mergeable, branchable distributed data stores.


  • Built-in snapshotting - backup and restore
  • Storage agnostic - you can use Irmin on top of your own storage layer
  • Custom datatypes - (de)serialization for custom data types, derivable via ppx_irmin
  • Highly portable - runs anywhere from Linux to web browsers and Xen unikernels
  • Git compatibility - irmin-git uses an on-disk format that can be inspected and modified using Git
  • Dynamic behavior - allows the users to define custom merge functions, use in-memory transactions (to keep track of reads as well as writes) and to define event-driven workflows using a notification mechanism


Documentation can be found online at


To install Irmin, the command-line tool and all optional dependencies using opam:

opam install irmin-unix

A minimal installation, with no storage backends can be installed by running:

opam install irmin

To only install the in-memory storage backend:

opam install irmin-mem

The following packages have been made available on opam:

  • irmin - the base package, no storage implementations
  • irmin-chunk - chunked storage
  • irmin-fs - filesystem-based storage using bin_prot
  • irmin-git - Git compatible storage
  • irmin-graphql - GraphQL server
  • irmin-http - a simple REST interface
  • irmin-mem - in-memory storage implementation
  • irmin-mirage - mirage compatibility
  • irmin-mirage-git - Git compatible storage for mirage
  • irmin-mirage-graphql - mirage compatible GraphQL server
  • irmin-unix - unix compatibility
  • irmin-pack - compressed, on-disk, posix backend
  • ppx_irmin - PPX deriver for Irmin content types (see

For more information about an individual package consult the online documentation.

Development version

To install the development version of Irmin, clone this repository and opam install the packages inside:

git clone
cd irmin/
opam install .


Below is a simple example of setting a key and getting the value out of a Git based, filesystem-backed store.

open Lwt.Infix

(* Irmin store with string contents *)
module Store = Irmin_unix.Git.FS.KV(Irmin.Contents.String)

(* Database configuration *)
let config = Irmin_git.config ~bare:true "/tmp/irmin/test"

(* Commit author *)
let author = "Example <>"

(* Commit information *)
let info fmt = ~author fmt

let main =
  (* Open the repo *)
  Store.Repo.v config >>=

  (* Load the master branch *)
  Store.master >>= fun t ->

  (* Set key "foo/bar" to "testing 123" *)
  Store.set_exn t ~info:(info "Updating foo/bar") ["foo"; "bar"] "testing 123" >>= fun () ->

  (* Get key "foo/bar" and print it to stdout *)
  Store.get t ["foo"; "bar"] >|= fun x ->
  Printf.printf "foo/bar => '%s'\n" x

(* Run the program *)
let () = main

The example is contained in examples/ It can be compiled and executed with dune:

$ dune build examples/readme.exe
$ dune exec examples/readme.exe
foo/bar => 'testing 123'

The examples/ directory also contains more advanced examples, which can be executed in the same way.


The same thing can also be accomplished using irmin, the command-line application installed with irmin-unix, by running:

$ echo "root: ." > irmin.yml
$ irmin init
$ irmin set foo/bar "testing 123"
$ irmin get foo/bar

irmin.yml allows for irmin flags to be set on a per-directory basis. You can also set flags globally using $HOME/.irmin/config.yml. Run irmin help irmin.yml for further details.

Also see irmin --help for list of all commands and either irmin <command> --help or irmin help <command> for more help with a specific command.


Feel free to to report any issues using the Github bugtracker.


See the LICENSE file.


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

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