Heroku published an article preaching polyglot persistence through a Database-as-a-Service approach:

Database-as-as-service is one of the coming decade’s most promising business models. […] DaaS also goes hand-in-glove with polyglot persistence. Thanks to database services, you won’t need to learn how to sysadmin/DBA for every datastore you use – you can instead outsource that job to a service provider specializing in each database.

While it definitely sounds exciting to be able to use all these NoSQL databases , we should always keep in mind the cost of complexity even if DaaS will help alleviate some of the complexity of heterogeneous systems.

The article includes also some interesting use cases for a couple of NoSQL databases:

• Frequently-written, rarely read statistical data (for example, a web hit counter) should use an in-memory key/value store like Redis, or an update-in-place document store like MongoDB.
• Big Data (like weather stats or business analytics) will work best in a freeform, distributed db system like Hadoop.
• Binary assets (such as MP3s and PDFs) find a good home in a datastore that can serve directly to the user’s browser, like Amazon S3.
• Transient data (like web sessions, locks, or short-term stats) should be kept in a transient datastore like Memcache. (Traditionally we haven’t grouped memcached into the database family, but NoSQL has broadened our thinking on this subject.)
• If you need to be able to replicate your data set to multiple locations (such as syncing a music database between a web app and a mobile device), you’ll want the replication features of CouchDB.
• High availability apps, where minimizing downtime is critical, will find great utility in the automatically clustered, redundant setup of datastores like Casandra and Riak.

These are good examples, but you can find many more in our coverage of NoSQL uses cases and the per-product case studies: CouchDB case studies or MongoDB case studies, etc.

Heroku Encourages Polyglot Persistence originally posted on the NoSQL blog: myNoSQL

via: http://blog.heroku.com/archives/2010/7/20/nosql/