Business Logic: Database or Application Layer

Question

The age old question. Where should you put your business logic, in the database as stored procedures ( or packages ), or in the application/middle tier? And more importantly

Answer 1

The only thing that goes in a database is data.

Stored procedures are a maintenance nightmare. They aren't data and they don't belong in the database. The endless coordination between developers and DBA's is little more than organizational friction.

It's hard to keep good version control over stored procedures. The code outside the database is really easy to install -- when you think you've got the wrong version you just do an SVN UP (maybe an install) and your application's back to a known state. You have environment variables, directory links, and lots of environment control over the application.

You can, with simple PATH manipulations, have variant software available for different situations (training, test, QA, production, customer-specific enhancements, etc., etc.)

The code inside the database, however, is much harder to manage. There's no proper environment -- no "PATH", directory links or other environment variables -- to provide any usable control over what software's being used; you have a permanent, globally bound set of application software stuck in the database, married to the data.

Triggers are even worse. They're both a maintenance and a debugging nightmare. I don't see what problem they solve; they seem to be a way of working around badly-designed applications where someone couldn't be bothered to use the available classes (or function libraries) correctly.

While some folks find the performance argument compelling, I still haven't seen enough benchmark data to convince me that stored procedures are all that fast. Everyone has an anecdote, but no one has side-by-side code where the algorithms are more-or-less the same.

[In the examples I've seen, the old application was a poorly designed mess; when the stored procedures were written, the application was re-architected. I think the design change had more impact than the platform change.]