Which is the most suitable Key-Value Store for a RDBMS background person?

Question

Is there a distinct winner among all the key-value stores? Cassandra, MongoDB, CouchDB? and do they all follow some central guidelines? or they all have their own say in defining their APIs.

I'm asking this question, especially from a perspective of a RDBMS skilled person who is new to key-value stores. Which one should we follow to best grasp the understanding/usage of this field?

We know about the RDMS from their theories that all available DBs (Oracle, SQL Server, ..) will have all the artifacts e.g. Tables, Indexes, Foreign keys etc. The only difference in these is the efficiency, security, features.

How can I know about the universal theory of these document-centered Databases and know what are the minimal artifacts that all these DBs (Mongo, Couch etc.) will have?

Answer 1

I work on MongoDB so I'm biased that way, but I think it is a nice combination of the things you're used to with an RDBMS (like dynamic queries and secondary indexes) and the performance and scalability of a key-value store.

Cassandra has a nice distributed model but afaik doesn't support secondary indexes. The document data model support by Mongo and Couch also allows for a little bit more complexity than the tabular model Cassandra uses.

One of the big differences between Mongo and Couch is the way queries are constructed. Couch uses a cool map/reduce mechanism, but your queries must be defined in advance. Mongo uses a more traditional dynamic query model that is more like what you're used to in an RDBMS.