The Guardian’s Mat Wall has spoken here at Qcon London about why it is migrating its web site away from Oracle and towards MongoDB.

He also said there are moves towards cloud hosting, I think on Amazon’s hosted infrastructure, and that its own data centre can be used as a backup in case of cloud failure – an idea which makes some sense to me.

So what’s wrong with Oracle? The problem is the tight relationship between updates to the code that runs the site, and the Oracle database schema. Significant code updates tend to require schema updates too, which means pausing content updates while this takes place. Journalists on a major news site hate these pauses.

MongoDB by contrast is not a relational database. Rather, it stores documents in JSON (JavaScript Object Notation) format. This means that documents with new attributes can be added to the database at runtime.

Although this was the main motivation for change, the Guardian discovered other benefits. Developer productivity is significantly better with MongoDB and they are enjoying its API.

Currently both MongoDB and Oracle are in use. The Guardian has written its own API layer to wrap database access and handle the complexity of having two radically different data stores.

I enjoyed this talk, partly thanks to Wall’s clear presentation, and partly because I was glad to hear solid pragmatic reasons for moving to a NoSQL data store.