Another option is to use real-time event-driven data processing to create an extract, transform, and load (ETL) based platform for a highly scalable data migration. As an example, we previously built a solution that allows data to flow from a live PostgreSQL database to a WordPress MySQL database through the use of the REST API and stubbing out objects in a Firestore database. The flow of data was done in a performant and reliable manner that utilized parallel processing and fault tolerance by using Cloud Functions, Firestore, and App Engine to ingest, map, and transform data as each table is read. Essentially rebuilding the WordPress database in real-time, from a massive PostgreSQL database that contained decades of data, in just a few minutes.