Databases no longer shared resources?

One interesting trend that I've noticed in many of the organizations that I've been into is that increasingly databases are being built to serve single applications. The early visions of databases shared amongst multiple applications is no longer the first choice. To a certain extent this has always been the case for certain operational systems, but now the reach of single application databases has grown. You'll even find data replicated across multiple multi-terabyte data warehouses to support different business intelligence solutions.

One reason for this trend could be that disk is seen as a cheap resource and there is no longer the cost constraint for minimizing the number of copies of data. Obviously this is not the full story as there is a cost to keep these different versions of data in sync, although this may not always be necessary. Given the synchronization cost, it seems the real driver for why single application databases are becoming more and more popular is the need for business agility. I think businesses can no longer be held to ransom by the database when they perceive the need to update an application to improve business performance.

In a shared database environment, making a change to an application that requires changes to the underlying database can be an extremely costly and time-consuming business. Just take a look at the excellent book Refactoring Databases: Evolutionary Database Design if you want to better understand the various impacts of making changes at the data layer. By moving to single application databases, all these complexities can be removed and business can update their business applications at the rate that the market demands rather than at the pace the database allows.

This move also fits in with the agile development practices which have been coming to the fore in the development community in recent years. I'm sure that time and again business guys have asked for updates to applications and the developers have said "sure" only to be blocked by what was going on in the database layer. That is not to say that changes are not possible in a traditional shared database environment, as Refactoring Databases shows, but without introducing single application databases you are not going to be able to run as fast as the business guys want.