mamulengo

A lightweight database based on datascript and a pluggable storage for data durability. In fact, mamulengo has probably poor performance when compared to other solutions and its purpose is small-sized applications that need an embedded database to get its business moving.

We use datascript as the main database, but write every transaction to a durable storage. Therefore, because of this simple addition we are able to provide two features to improve datascript and enable it to be a full-fledged immutable database: i)durability and ii) time-travel feature as in Datomic.

Mamulengo supports PostgreSQL and H2 for Clojure and Local Storage for ClojureScript.

Release and Dependency Information

This project follows the version scheme MAJOR.MINOR.COMMITS where MAJOR and MINOR provide some relative indication of the size of the change, but do not follow semantic versioning. In general, all changes endeavor to be non-breaking (by moving to new names rather than by breaking existing names). COMMITS is an ever-increasing counter of commits since the beginning of this repository.

Installation

Bleedinng-edge project.. Still wondering about APIs and code organization..

Leinigen/Boot

[mamulengo "0.1.44"]

Clojure CLI/deps.edn

mamulengo {:mvn/version "0.1.44"}

Usage

(require '[mamulengo.core :as m])

(def cfg {:durable-storage :postgresql
          :durable-conf {:dbtype "postgresql"
                         :dbname "mamulengo"
                         :password "test"
                         :user "test"}})

;;; let's define a schema
(def schema-planets
  {:body/name {:db/cardinality :db.cardinality/one
               :db/unique :db.unique/identity}
   :body/diameter {:db/cardinality :db.cardinality/one
                   :db/unique :db.unique/identity}})

(m/connect! cfg schema-planets)


;;; now you are ready to save your data!!
(m/transact! [{:db/id -1
                     :body/name "Earth"
                     :body/diameter 12740}
                    {:db/id -2
                     :body/name "Pluto"
                     :body/diameter 80}
                    {:db/id -3
                     :body/name "Venus"
                     :body/diameter 12100}])

;;; you should also retrieve it back!
(m/query! '[:find (pull ?e [*])
            :in $ ?n
            :where
            [?e :body/name ?n]]
            ["Pluto"])

Time travel

Right now only the Local Storage option has support for time-travel. The API behaves similarly with Datomic one, you can pass an old Database/Connection object to the query function.

(def ret (m/transact! {:body/name "Wow"}))  ;; => db-before... db-after..

;;; more things happening...

(m/query! '[:find ?name
            :where [?e :body/name ?name]]
            (:db-before ret))

This will query the db-before database. You can also use m/get-database to capture a specific version of the database based on timestamp.

(def old-db (m/get-database! #inst "2020-02-18T11:46:31.505-00:00"))

Why mamulengo?

In Brazilian culture we have a very famous event in the northeast region called mamulengo which is a puppet theater. In front of the public we have the puppets that entertain and captivate the audience and behind it we have the hands of the artist that brings movements and voice to the puppets.

Mamulengo here has the same objectives, we want you to be amazed by datalog query engines and all the bells and whistle of immutable databases, but behind the scenes we manage the hard work to make this possible with no overhead introduced to the audience.

Ideas

The idea came from Rodolfo Ferreira about rethinking some concepts on databases and reaching the conclusion that not all applications need an insane amount of write/reads per second. Sometimes we only need a SQLite to do our work and go home happily.

However, we still want the advantages of Datascript and Immutable data sources.

The very initial code was inspired in https://gitlab.com/kurtosys/lib/factoidic.

License

Copyright © 2020 Wanderson Ferreira

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.