Migrating database systems containing transactional histories can feel like changing the engines on a plane mid-flight. When the cost of database downtime can exceed thousands of dollars per minute, traditional offline migration pipelines are simply out of the question.
The answer lies in incremental decoupling using the **Strangler Fig Pattern** combined with transactional event sourcing.
First, set up a change data capture (CDC) stream using tools like Debezium. This replicates data continuously to the new datastore. Second, utilize a dual-write mechanism in the application layer. Code reads from the old database but writes changes asynchronously to both databases. Finally, toggle a feature flag to shift reads to the new datastore, minimizing risk at every step.