Has anyone seen or implemented a CRUD application in Clojure using a
database of immutable facts?
For instance, a traditional database table supporting a todo-list
application has columns
user_id, task_id, task_description, is_done
A new row is created when a user adds a task.
Then that row is updated so is_done = TRUE when the user checks the
task off.
With immutable facts this would instead be a collection of statements:
User U added task T with description D at time T1
User U completed task T at time T2
To get a list of unfinished tasks for a user, you'd need to grab all
the tasks from this "transaction log", put them into a data structure,
and then remove ones when you learn that they've been completed.
Whatever is left over is the todo list.
Nathan Marz talked about this in terms of big data:
http://nathanmarz.com/blog/how-to-beat-the-cap-theorem.html
and Datomic's big bet is that your life as a developer gets much
easier when you just deal with (entity, attribute, value) + time.
I buy it in theory, but I have no idea what to expect in terms of
performance (e.g., how long would it take to find the current todo
list of someone who has added and completed/removed a few thousand
items?).
Has anyone implemented this idea on Clojure datastructures using,
say, (timestamp, keyseq, value) and reducing a ton of calls to assoc-
in?
Aside from speed, what are some other tradeoffs of an immutable
approach?
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