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Before going into Change Data Capture (CDC) on Amazon Web Service Database Migration Service (AWS DMS), a look at each is required. CDC identifies and captures the changes and modifications that have been made in the latest production data or metadata. The changes are registered in specific time gaps often in minutes and seconds. These changes are then copied into a separate data repository by replication software. CDC batch load replication ensures that the target remains always synchronized after completion of each load. As in batch loads, CDC enables replication software in copying one source to one or multiple targets. Now coming to the other part – AWS DMS - inAWS DMS CDC, it is a cloud-based service that enables easy migration of relational databases, data warehouses, NoSQL databases, and more. AWS DMS can also be used for migrating data into the AWS cloud or any combination of on-premises setups and the cloud. It is also possible to carry out one-time migrations or replicate changes to keep data in sources and targets in sync. Because AWS DMS is a part of the AWS cloud, all the benefits of AWS services like cost efficiency, speed to market, security, and flexibility is available.
You can create an AWS DMS CDCtask for capturing current changes to the source data store while migrating your data. This process can also be done after completion of the initial full migration to a supported target store. This is commonly known as ongoing replication and is used when replicating ongoing changes from a source data store. It works by collecting changes to the database logs by utilizing the database engine’s native API. Regardless of whether the task is a CDC-only task or a full-load task which starts CDC only after it is completed, the migration process has only tables from the source. In full-load only task though, it is possible to migrate views or a combination of views.
For reading current changes from the source database, AWS DMS CDCuses engine-centric API actions from the source engine’s transaction logs. Following is a snapshot of how it is usually done. · For Microsoft SQL Server, AWS DMS uses MS-Replication or MS-CDC to enter information to the SQL Server transaction log. · For Oracle, AWS DMS CDC uses either the Oracle LogMiner API or the binary reader API to track ongoing changes. AWS DMS reads ongoing changes from the online or archived redo logs based on the SCN (System Change Number).
· For MySQL, AWS DMS reads changes from the row-based binary logs and loads them to the target. · For PostgreSQL, AWS DMS uses the test_decodingplugin and sets up logical replication slots to track changes from the source and migrate them to the target. · For Amazon RDS it is advisable to ensure AWS DMS CDCin backups. This is the functioning of CDC in AWS DMS