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.

About

• 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

API documentation can be found online at https://mirage.github.io/irmin

Installation

Prerequisites

Please ensure to install the minimum opam and ocaml versions. Find the latest version and install instructions on ocaml.org.

To install Irmin with the command-line tool and all unix backends using opam:

  opam install irmin-cli

A minimal installation containing the reference in-memory backend can be installed by running:

  opam install irmin

The following packages have are available on opam:

• irmin - the base package, plus an in-memory storage implementation
• irmin-chunk - chunked storage
• irmin-cli - a simple command-line tool
• irmin-fs - filesystem-based storage using bin_prot
• irmin-git - Git compatible storage
• irmin-graphql - GraphQL server
• irmin-http - a simple REST interface
• irmin-mirage - mirage compatibility
• irmin-mirage-git - Git compatible storage for mirage
• irmin-mirage-graphql - mirage compatible GraphQL server
• irmin-pack - compressed, on-disk, posix backend
• ppx_irmin - PPX deriver for Irmin content types (see README_PPX.md)
• irmin-containers - collection of simple, ready-to-use mergeable data structures

To install a specific package, simply run:

  opam install <package-name>

Development Version

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

  git clone https://github.com/mirage/irmin
  cd irmin/
  opam install .

Usage

Example

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

open Lwt.Syntax

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

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

(* Commit author *)
let author = "Example <[email protected]>"

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

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

  (* Load the main branch *)
  let* t = Store.main repo in

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

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

(* Run the program *)
let () = Lwt_main.run main

The example is contained in examples/readme.ml 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.

Command-line

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

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

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.

Issues

Feel free to report any issues using the GitHub bugtracker.

License

See the LICENSE file.

Acknowledgements

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