When to use CouchDB vs RDBMS
couchdb, database, rdbms
Solution
I recently attended the NoSQL conference in London and think I have a better idea now how to answer the original question. I also wrote a blog post, and there are a couple of other good ones.
Key points:
- We have accumulated probably 30 years knowledge of adminstering relational databases, so shouldn't replace them without careful consideration; non-relational data stores are less mature than relational ones, and so are inherently more risky to adopt
- There are different types of non-relational data store; some are key-value stores, some are document stores, some are graph databases
- You could use a hybrid approach, e.g. a combination of RDBMS and graph data store for a social software site
- Document data stores (e.g. CouchDB and MongoDB) are probably the closest to relational databases and provide a JSON data structure with all the fields presented hierarchically which avoids having to do table joins, and (some might argue) is an improvement on the traditional object-relational mapping that most applications currently use
- Non-relational databases support replication (including master-master); relational databases support replication too but it may not be as comprehensive as the non-relational option
- Very large sites such as Twitter, Digg and Facebook use Cassandra, which is built from the ground up to support clustering
- Relational databases are probably suitable for 90% of cases
In summary, consensus seems to be "proceed with caution".
Problem
I am looking at CouchDB, which has a number of appealing features over relational databases including: - intuitive REST/HTTP interface - easy replication - data stored as documents, rather than normalised tables I appreciate that this is not a mature product so should be adopted with caution, but am wondering whether it is actually a viable replacement for an RDBMS (in spite of the intro page saying otherwise - http://couchdb.apache.org/docs/intro.html). - Under what circumstances would CouchDB be a better choice of database than an RDBMS (e.g. MySQL), e.g. in terms of scalability, design + development time, reliability and maintenance. - Are there still cases where an RDBMS is still clearly the right choice? - Is this an either-or choice, or is a hybrid solution more likely to emerge as best practice?