Most people think transferring and adjusting schemas, or copying the data from one system to another are the difficult challenges in a migration. Sure, these are tasks that require expertise, efficiency, and the right set of tools; they can be highly system-specific and are certainly no trivial matter but this aspect of data migration is just the tip of the iceberg. A good DBA team may get this task completed in a few weeks, will hook up the data loads, and have you up and “running”.
Not only are you not done yet, but you just reached the point where it gets more challenging. In the second stage of a migration, all applications that previously used the old system need to be brought over to the new one. And it is this task that consumes almost 85% of your migration budget!
Every application requires replacing drivers, reconfiguring the app, or even modifying the queries to work with the new system. This is a highly labor-intensive process that offers plenty of room for errors. Multiply this effort by a few tens, or even hundreds, of applications and you quickly understand why migrations are often multi-year efforts, routinely overrun budgets, or fail altogether.
We call this the “Migration Paradox” because most people are just perplexed to find out the cost breakdown is completely counter-intuitive: moving the actual database, its data, and the load processes is the simple part of the exercise! Moving the applications, that’s your big challenge.