VietMX Staff asked 3 years ago
The main difference is that document stores (e.g. MongoDB and CouchDB) allow arbitrarily complex documents, i.e. subdocuments within subdocuments, lists with documents, etc. whereas column stores (e.g. Cassandra and HBase) only allow a fixed format, e.g. strict one-level or two-level dictionaries.
For example a document-oriented database (like MongoDB) inserts whole documents (typically JSON), whereas in Cassandra (column-oriented db) you can address individual columns or supercolumns, and update these individually, i.e. they work at a different level of granularity. Each column has its own separate timestamp/version (used to reconcile updates across the distributed cluster).
The Cassandra column values are just bytes, but can be typed as ASCII, UTF8 text, numbers, dates etc. You could use Cassandra as a primitive document store by inserting columns containing JSON – but you wouldn’t get all the features of a real document-oriented store.
