Wallet must work all the time—even during a migration. Amazon sought to eliminate any impact on customer transactions, maintain complete data consistency, and avoid a code or database schema “freeze” that would interrupt the adoption of new features.

To meet these goals, the migration was performed in three steps. First, in parallel with Oracle persistence, the Wallet team created the DynamoDB persistence layer. Operations were executed on both databases at once, one for the customer transaction and one for verification.

Second, the team migrated all records from Oracle to DynamoDB. The dual read/write setup guaranteed that all new records were created in both databases, meaning that only missing records had to be migrated. The team identified the instances in which transactions failed in one of the databases and recovered them to ensure full consistency.

Third, after the team verified that all records were successfully migrated, Amazon switched the DynamoDB database to the primary role. After running DynamoDB as the primary database for some time, the team disconnected the Oracle database. The migration process met all the team’s requirements, including zero downtime and zero customer impact, with more than 10 billion records migrated from eight Oracle tables to six DynamoDB tables.