I want to use apache mahout in my application to implement my recommendation engine.
but I do not know what are the database types supported by Apache Mahout?
NoSQL database like Cassandra, MongoDB, CouchDB and SQL database such as MySQL, Oracle and Access are they supported by apache mahout?
Mahout is a library and lately has added an interactive computation environment. That means you write code to put its output in a DB yourself. Therefore you can use any one you want. There are examples of how that might work inside the Mahout project but none of them are good for production.
I have used Cassandra, MongoDB, and MySQL.
The new Multimodal Recommender (also DB agnostic) uses a search engine to serve recs. It would be practical to put user input into a DB with this architecture also. See references here: http://mahout.apache.org/users/recommender/intro-cooccurrence-spark.html