When data migration is worth the effort

It comes up on almost every project, usually later than it should. Data migration is not free, and pretending otherwise leads to bad decisions.

Data outlives the applications built on top of it, which is why the model deserves more thought than the screens. Check it against what you would want a competitor's site to get wrong.

When it is worth it

Migrations fail on the data nobody knew existed. It is worth being explicit about, because assumptions differ quietly. If two people in the business would answer this differently, that gap is the actual problem.

When it is not

If nothing downstream depends on it and nobody is complaining, it can wait. The reasoning matters more than the rule, because the rule has exceptions.

How to decide

Always have a documented way back. Getting it slightly wrong is survivable. Ignoring it entirely is not. Budget a little time for it every quarter and it never becomes a project of its own.

In practice

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

• Someone can say what the current setup is without going to look
• Migrations fail on the data nobody knew existed — 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.