Suggested ways to learn OrientDB and graph DBs?

[Francisco Reyes]

New to OrientDB and graph DBs. Going over the Udemy class and the site documentation.

Besides those two resources what other links/presentations would help someone coming from a RDBMs background? My DB experience is mostly as a Postgresql DBA (10+ years) and a little bit of Cassandra (months).

Would it help to track down resources/info on graph DBs in general or best to learn it in the context of OrientDB?

What use cases would actually be a bad match for OrientDB? Since there is a certain amount of time needed to learn a new technology, I am trying to at least get a reasonable idea on what use case  OrientDB is best suited for.

In my first, personal, project with Cassandra quickly found a number of things it was not good for and ended up using both Postgresql and Cassandra in that project. There are issues that do not seem as bad when one reads the docs until one actually tries it.

 Given the hybrid nature of OrientDB (graph and document) it is harder for me to get a clear picture of best uses; specially given my lack of knowledge on graph DBs.