Before you invest in a data warehouse

There is no clever trick in this one, just a handful of decisions worth making deliberately. Before you spend anything on a data warehouse, it is worth confirming a few things are already true.

Numbers get quoted in meetings long after anyone remembers how they were calculated. Budget a little time for it every quarter and it never becomes a project of its own.

Prerequisites

• You can describe the outcome you want in one sentence
• Someone owns it after the work is done
• Reporting queries and application queries want different shapes
• You have a way to tell whether it worked

What to watch for

Separating them stops reports taking the product down. In practice this is a scheduling problem more than a technical one. It is the sort of thing that looks like polish right up until it costs you an enquiry.

Start with the questions, not with the schema. There is a version of this that is over-engineered, and it is worth avoiding. If two people in the business would answer this differently, that gap is the actual problem.

The short version

Most data problems are ownership problems that turned into technical ones. Three things worth confirming about a data warehouse before you move on:

• Someone can say what the current setup is without going to look
• Reporting queries and application queries want different shapes — and you know whether that is true here
• There is a way to tell whether the last change to this helped

The point is not perfection, it is knowing which of these you have consciously chosen to skip.