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README.md

perdure

Clojure's PERsistent data structures made DURable

Introduction

perdure persists a regular clojure atom to disk while keeping track of its previous versions.

As storage backend, perdure uses git, so you can use regular git commands (such as git log) to inspect the history.

perdure is a young project and should be considered alpha quality.

Usage

> git init data

Initialized empty Git repository in /home/paulus/prg/perdure/data/.git/

> lein repl

Create a git-backed atom

user=> (def a (git-atom []))
W  3ea457ad900cbf1528fb25f49ee5c615a8dc94df
#'user/a

Update the atom. When you swap!, a new commit is created automatically.

user=> (e/swap! a conj {:name "Joe" :age 40})
W  2d97424b9230c0a15c4dc9119baf03845ac5fa7e
W  1a6407c61334a17925efb362efe522b8042e3c9f
[{:age 40, :name "Joe"}]

user=> (e/swap! a conj {:name "Bob" :age 20})
c  2d97424b9230c0a15c4dc9119baf03845ac5fa7e
W  2ba7383f307fda97cd2aa643ea19f5118bbfd07d
W  5b66859433b541c21c75fdb5bf37c2911c127ee5
[{:age 40, :name "Joe"} {:age 20, :name "Bob"}]

Note that we only need to write the collections that have changed and their parents.

user=> (e/swap! a update-in [0 :age] inc)
W  5ae443ab3272eac28214a848c946a5da55c2914c
c  2ba7383f307fda97cd2aa643ea19f5118bbfd07d
W  f17f288b0ad6f974ac481b5666e10a200f89fdf6
[{:age 41, :name "Joe"} {:age 20, :name "Bob"}]

We can use git commands:

> git log
commit 8955b43a0e9a5840a6ea000c5ad5db10ae974601
Author: Paulus Esterhazy <pesterhazy@gmail.com>
Date:   Wed Apr 8 18:23:39 2015 +0200

    Perdure initial commit

commit 4e6b985c13aef738d6105915c9203246e0cd9461
Author: Paulus Esterhazy <pesterhazy@gmail.com>
Date:   Wed Apr 8 18:22:14 2015 +0200

    Perdure initial commit

commit 5b82a2b48fc975613a12a0cbb3b54825945bf940
Author: Paulus Esterhazy <pesterhazy@gmail.com>
Date:   Wed Apr 8 18:21:40 2015 +0200

    Perdure initial commit

commit ba3f8db6c0ef7acc839d6cb514dda39be6a411b8
Author: Paulus Esterhazy <pesterhazy@gmail.com>
Date:   Wed Apr 8 18:19:27 2015 +0200

    Perdure commit

We can inspect what has changed using familiar notation:

> git diff 'HEAD^'

diff --git a/0/root b/0/root
index 6845dd9..b77155c 100644
--- a/0/root
+++ b/0/root
@@ -1,4 +1,4 @@
 {
-:age 40
+:age 41
 :name "Joe"
 }
diff --git a/root b/root
index 89fdfce..2a65de7 100644
--- a/root
+++ b/root
@@ -1,4 +1,4 @@
 [
-#pesterhazy.perdure.core/rf "2d97424b9230c0a15c4dc9119baf03845ac5fa7e"
+#pesterhazy.perdure.core/rf "5ae443ab3272eac28214a848c946a5da55c2914c"
 #pesterhazy.perdure.core/rf "2ba7383f307fda97cd2aa643ea19f5118bbfd07d"
 ]

Related work

perdure builds on enduro by Alan Dipert.

Contact

Contact: pesterhazy@gmail.com or @pesterhazy on Twitter

License

Copyright © 2015 Paulus Esterhazy

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.

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