And also, probably I should better explore website, but is it transactional? In other words, is it possible to save multiple documents and RethinkDB server will reject them in case of conflict, just like all-or-nothing semantic in couchdb before ver. 0.9?
JSON docs are stored in tables -- a table is just a collection of JSON documents. We of course also support arrays, but the reason why we start with tables as a primitive is that it allows doing significant optimizations that otherwise would be very hard/impossible. If the entire DB was one huge JSON document, optimizations would be much more difficult to do. Grouping docs into tables essentially gives the system a hint as to the usage intent.
is it transactional?
Only for changes on a single document. There are no transactional guarantees on queries that touch more than one document.
Any plans to change it in future?