Database Migration Service lets you migrate data to a Cloud SQL destination instance,
and then set up cascading read replicas for that instance.
Cascading read replicas
let you create a read replica under a Cloud SQL read replica in the same or
different region before promoting your instance to primary. You can add up to four
levels of cascading read replicas, including the primary instance.
Cascading read replicas in Cloud SQL for MySQL are supported only for
global transaction identifier (GTID)-based replication.
If you want to use cascading read replicas in your migration,
set GTID_MODE to ON on your source instance.
Set up cascading read replicas
To migrate your data to a Cloud SQL destination that is using cascading read
replicas:
Wait until the full dump phase of the job completes and the migration job
enters the change data capture (CDC) phase. Your migration job is in the CDC
phase when the Status column in the Migration jobs page indicates a CDC
substatus.
Once in the CDC phase, you can set up your cascading read replica. For
information about how to create cascading read replicas for a Cloud SQL destination
instance, see Set up a cascading replica.
You can promote your Cloud SQL replica to primary instance using Database Migration Service.
For information about promoting a destination instance, see
Promote a migration.
When you promote the Cloud SQL replica to a primary instance, the replica's cascading
replica hierarchy is retained.
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