Overview
Continuous migration
Continuous (sometimes referred to as ongoing or online) migration is a continuous flow of changes from a source PostgreSQL database to an AlloyDB for PostgreSQL destination that follows an initial full dump and load. In the case of a migration, when the time comes to switch to use the destination for reads and writes, perform apromote operation. Promotion means that the destination instance is disconnected from the source, and is promoted from a replica instance to a primary instance.
Continuous migration follows these steps:
Initially, a snapshot is taken of the source database. This incurs a short (under 10 seconds) lockout on the database tables, one at a time, as the dump is created. The source can continue accepting writes.
After the initial dump is taken, it's loaded into the destination.
After the load is completed, the ongoing changes (also known as change data capture or CDC) are processed.
When the time comes to switch to using the destination, stop writing to the source and initiate a promotion. This allows the application to read and write against the destination database.
Dependent applications can experience downtime for at least the duration of the replication delay at the time of the decision to promote.
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Last updated 2026-03-10 UTC.