I started out planning to write an entry I was going to title 'when I reach for a relational database'. The problem with this implicit question is that in practice the answer is 'when the system I'm building on basically insists on it'. Otherwise I basically don't use one, even when the problem more or less naturally fits into a relational world. On a purely logical basis, this is crazy; using a relational database for relational things is much easier than the alternatives and SQLite makes this trivial.

In thinking about it, I've come around to the idea that my problem with relational databases is that using a database makes my data relatively opaque and as a result complicates my life. The easy option for a relational database is an SQL based database, probably SQLite, and all of those store my data in unreadable and uneditable binary files. In order to get at my data I need to use the database server's tools (or write code). The direct consequence of this is that I can't inspect and go through my data by firing up less or grep or any number of other things and I can't (if I want to) put things under version control in any easy way.

The slightly more indirect consequence is that I need to write more tools. When my data is in plain text files I can modify my data with an editor or other simple Unix programs; add something, delete something, modify something, shuffle things around, it's all something that gets done with existing Unix programs and maybe some thin scripts. When my data is in a SQLite database I have to manipulate the data through SQLite in some way, either in more complicated shell scripts that drive the SQLite shell or through actual little utility programs that I write. In practice the latter is much safer and so what I'm likely to wind up with. Either way it's more work and more dedicated tools that I have to keep track of in various ways.

For me all of this adds friction to using a real relational database, enough friction that I'll endure some level of pain from hacking things together with plain text files instead. This is not completely rational, but evidently I put a high premium on being able to see things with less and edit them with vi.

(Note that some people have violent objections to relational databases, either in general or for uses where they aren't 'needed' in some sense. I'm not one of them; I don't have any strong feelings that they're inelegant or consume too many resources or whatever.)