Data Mining in a Django/Postgres application

You might want to consider Cube. It is not a Django app, but it has a lot of nice features baked in, and Django can communicate to it easily. Also, it is lovely.

You could have you Django app just blast off events into MongoDB when the occur. This separation of systems would prevent any additional strain on your Django app.

Sorry Mridang Agarwalla, some times your question come back to mind ...

I thought the way to keep in sync both databases, OLAP and OLTP, up to date with low impact in OLTP.

In 2002 I successfully employed this technique for a similar issue. It works as follows:

1. You write a trigger for each fact table. When fact data is modified trigger inserts a row in a table that reflects this event (idEvent + update | delete | insert + foreign key to fact table).
2. A low priority daemon do a infinite loop, for each loop iteration you 'pop' 10 events from table and update OLAP database with this new information.

You can optimize daemon behavior, for example, if table don't has new events daemon can sleep for 15 seconds.

In my escenario only fact tables have trigger. If fact table reference data that no is in OLAP database I created the data at this time (OLTP and OLAP has different schema).

If you analize your database you can find hundred of tables but only few tables are really fact tables.

Well, I konw this is only a partial answer of your answer. Second part of your question talk about a power tool to analize data. I can't suggest to you any open source product (because I have not experience with open source analysis tools). I have worked with Microsoft Analysis Services + Tableau software in frontend. This is a very nice solution but I don't know if it matches with your filosofy. For data minning you have KNIME (Konstanz Information Miner) that is a user-friendly and comprehensive open-source data integration, processing, analysis, and exploration platform (but you need a previus ETL task).

Please, sent to me news about your project, I'm very interested. I have a django student attendance solution and I want to add analysis functionality.