Using both graph db and document db

Question

I'm considering a setup where I have entities stored both in a document db (e.g. CouchDB) and a graph db (e.g. Neo4j). The rationale is storing each entity information (data, blobs, values, complex internal structure) in the document db while storing the entity relations (parents, children, associated entities) in the graph db.

Has anyone done / seen / been bitten by a setup like this? What kind of issues should I expect? First thing that come to mindaka the 2-phase commit. But backups are problematic too here.

Answer 1

Ran,

Since CouchDB and most (all?) of the document/ kv stores do not support transactions, you would need to stop worrying about 2-phase-commits. You can do XA transactions between Neo4j and MySQL for example, but not CouchDB or it's relatives.

Indeed, for simplicity's sake, why not a pure graph database architecture? You get the better expressiveness and transactions - what is the rationale of adding another moving part in the form of a second store type?

Answer 2

You may check out the book "Seven DBs in Seven Weeks". 8th chapter talks about building up a polyglot structure via CouchDB, Neo4j and Redis.