Parallel Change
Parallel change a.k.a as Expand and Contract, is a technique used to make changes in a system without causing downtime or changes to the client immediately.
It's important to remember the sequence and keep in mind that at a given point in time, we will be supporting both the old and new versions of the system.
Not just a database concept
This is a generic concept and not just a database concept. Even though I have used it only in database migrations, this applies even to the application interface changes.
dual writes
Dual writes can be replaced using CDC as well. Then there is one step less for the application to do.
important links