How Does Delta Migration Work?

Perform an initial full migration to move all the data from the source to the target system.
After this first migration, the target system is up-to-date with the source.

Change Data Capture (CDC):
- This technique monitors source databases for changes and captures only the delta (new records, updated fields, or deleted rows).
- Tools: Apache Kafka, AWS DMS, Debezium, Oracle GoldenGate.
Log-based Replication:
- Use transaction logs or logs to identify the changes (inserts, updates, deletes) in the source system.
- The logs capture delta changes and are pushed to the target.

Once changes are tracked, the delta records are transferred to the target system.
This can happen on a scheduled basis (e.g., hourly, daily) or in real-time.

The target system is continually updated with the latest changes from the source.
At the end of the migration process, you may have a final cutover to switch fully to the new system.

Reduced Data Volume
- Only the changed data is moved, which significantly reduces the volume of data to be transferred, leading to faster migrations.
Minimized Downtime
- Since the initial migration has already transferred most of the data, delta migration can be executed in shorter windows, keeping downtime minimal.
Lower Costs
- Migrating less data leads to lower network usage and reduced resource consumption, making delta migration more cost-effective than a full migration.
Real-Time Sync
- Delta migration can be performed in real-time to keep the source and target systems synchronized.

Tracking Changes
- Implementing an effective change detection mechanism can be complex, especially with legacy systems that may not support CDC or transaction logs.
Data Integrity
- Ensuring data consistency and handling any discrepancies between the source and target during delta migration is crucial.
Handling Deletes
- If rows or records are deleted in the source, ensuring these deletions are accurately reflected in the target system can be tricky.
Concurrency Issues
- Changes occurring in the source system while delta migration is happening may lead to conflicts or data mismatches.

AWS Database Migration Service (DMS):
- Provides real-time replication and supports CDC for incremental migrations.
Debezium:
- An open-source platform for CDC that works with Kafka to track and replicate changes.
Oracle GoldenGate:
- A high-performance solution for real-time data integration and CDC for Oracle databases.
Apache Kafka:
- Often used with Debezium for event-driven delta migration.
SQL Server Replication:
- Allows transactional replication to move data incrementally between SQL Server instances.