A key to the kingdom

Agile talks about emergent architecture and building vertical slices of functionality. It is typically understood that all efforts must go toward creating valuable user-facing pieces, as opposed to delivering software layers that cannot be used until all other layers are in place.  Unfortunately, this approach is often taken as “all we need is the visible parts”, i.e. the parts that the user gets to see and click on, or that push the data to be displayed.

When I first encountered a large DB supporting a well-used, living application with no indexes or foreign keys, I thought it was a rare oversight.  Then I encountered a few more database setups just like it, with large and heavily used tables and relationships, but neither indexes nor keys defined.  In all cases, users were complaining about slow response times, and administrators remembered more than one instance of the application becoming non-responsive under heavy load as DB requests timed out en masse.

Other developers I talked to also mentioned that they worked with reasonably large DBs that were missing indexes and foreign keys. A number of people, working in different companies on unrelated projects, mentioned that their engineering managers or software architects absolutely refused all suggestions to create even primary keys on tables “since nobody sees them anyway”. Several developers talked about applications being re-implemented, in part, because of poor response times caused by frequent timeouts of DB requests.

Vertical slices of user-visible functionality must include “the plumbing” that allows the application to handle the expected load. “Emergent architecture” is not complete without at least basic considerations of technical quality. A project cannot succeed without understanding what it takes to deliver user value in a production situation – and that typically includes multiple users working simultaneously.  Building in proper DB infrastructure is a simple example of such considerations, the work that is not visible but nevertheless valuable to the user.