Datomic is intriguing and powerful but I'd be reluctant to use a proprietary database developed by such a small company. I think Riak has a better model for free/paid usage. There is nothing like Datomic but there are so many excellent open-source databases these days.
I agree completely; we are looking at tech choices for a new project and Datomic is an excellent fit for the way we want our systems to work, but we're just not comfortable with the closed/paid model, especially for such a young product. For now we are looking at ways to use an accumulation based system (vs update-in-place) in PostgreSQL. If anyone has any experience with this I'd love to hear about it!
There is another database which can be used in the 'accumulation-based' space: http://geteventstore.com
It has the same main drawbacks as Datomic - it's young and multi-node deployment comes with commercial plan only, however it's really fast and easy to work with once you embrace the event-sourcing programming model.
I'm the dev for an open source event-based database called Sky (http://skydb.io). Similar data model but it's aimed at a different use case than Datomic -- it's primarily used for analytics. The event data model is nice for avoiding conflicts but it's an up road battle to try and replace traditional relational databases. I find that storing historical events is primarily useful for either analytics or auditing. It makes more sense to move that off your primary data store if possible.
I do find that making databases smarter about the data they hold can really provide some great optimizations. Sky can crunch through about 60MM events per second on a single core because it is built for event data models. I'm sure Datomic can probably get some good optimizations too. I'll be curious to see some benchmarks.
Here's a demo app of Sky crunching all the events in the GitHub Archive (starts around 3m:20s):
I'm working on multi-core distribution right now and I'll be doing multi-node after that. Check out the web site or GitHub (https://github.com/skydb/sky) for more information. It's MIT licensed so feel free to hack away.
I doubt very much that there is a timeline. It's a product and the last I heard was staying close sourced. Having said that, I would not be surprised if some of its libraries are open sourced. I know of at least one that is in the pipeline.
Datalog for clojure's data structures would take Clojure to a new productivity level. It would also greatly simplify a lot of the code out there today, further driving software to be more data-oriented. Data is the ultimate API. Please make it be Datalog.
Datomic Free gives you that capability right now, for free, no strings attached, and no need to use a Datomic db. Not open source, but free as in gratis, a la Creative Commons.
We may trim down the deps a bit for that use case.
A trimmed down version is great news. Datalog makes Clojure so much better! Ideally it would be part of Clojure itself, but I'll take what I can get :)
I'm working on a port of BloomL for clojure which will include a semi-naive datalog interpreter (it will already support naive, monotonic datalog by tonight). It will likely never be as well optimised as the Datomic libs but it is LGPL.
