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CowDB - Pure Key/Value database for Erlang Applications

Copyright (c) 2014-2015 Benoit Chesneau and the contributors.

Version: 0.4.2

Authors: Benoit Chesneau (


CowDB implements an indexed, key/value storage engine.


  • Append-Only b-tree using COW
  • Read/Write can happen independently
  • Put/Get/Delete/Fold operations support transactions (add, remove operations on a 1 ore more store at once) transaction functions: Transaction functions can atomically analyze and transform database values in a transaction. You can use them to ensure atomic read-modify-update processing, and integrity constraints.
  • Transaction log
  • Snapshots support: you are able to take a snapshot of the database at any time (until the database is compacted)
  • Destructive compaction to reclaim space in your database. The log history is lost during the transaction.
  • Automatic compaction


Look at the cowdb module for the API usage.

main CowDB website is

Build process

1. Install rebar

To build CowDB you need to install rebar in your PATH. Rebar is available on Github:

Follow the README to install it.

2. Build the sources

Fetch the source code:

    $ git clone

Build the source, run the make command. It will fetch all required dependencies.

    $ cd /<PATH_TO>/cowdb
    $ make

3. Run tests

    $ make test

Example of usage:

    1> {ok, Pid} = cowdb:open("testing.db").
    2> cowdb:put(Pid, a, 1).
    {ok, 1}
    3> cowdb:get(Pid, a).
    4> cowdb:mget(Pid, [a, b]).
    5> cowdb:put(Pid, b, 2).
    {ok, 2}
    6> cowdb:mget(Pid, [a, b]).
    7> cowdb:mget(Pid, [a, b, c, d]).
    8> cowdb:transact(Pid, [
        {add, c, 2},
        {remove, b},
        {fn, fun(Db) ->
                    {ok, {a, V}} = cowdb:get(Db, a),
                    [{add, d, V}] end}]).
    {ok, 3}
    9> cowdb:mget(Pid, [a, b, c, d]).
    10> cowdb:fold(Pid, fun(Got, Acc) -> {ok, [Got | Acc]} end, []).

Ownership and License

The contributors are listed in AUTHORS. This project uses the MPL v2 license, see LICENSE.

cowdb uses the C4.1 (Collective Code Construction Contract) process for contributions.


Under C4.1 process, you are more than welcome to help us by:

  • join the discussion over anything from design to code style try out
  • and submit issue reports
  • or feature requests pick a task in
  • issues and get it done fork
  • the repository and have your own fixes send us pull requests and even
  • star this project ^_^

To run the test suite:

    $ make test