Signs it is time to revisit a data warehouse

Teams tend to reach for this after something has already gone wrong. A few signals that a data warehouse is due some attention.

Numbers get quoted in meetings long after anyone remembers how they were calculated. Anything you cannot measure here, you are deciding by taste, which is fine as long as everyone knows it.

The signals

• Nobody can say when it was last reviewed
• The answer depends on who you ask
• Reporting queries and application queries want different shapes
• Separating them stops reports taking the product down

The practical version

Start with the questions, not with the schema. This is the sort of thing that compounds, quietly, in both directions. The practical test is whether someone new to the project could tell, in a minute, that it had been handled.

How to tell if yours is fine

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

None of this needs a rewrite. Most of it is a morning's work once someone decides to do it.