When using Debezium and Kafka Connect JDBC Sink Connector to replicate and synchronize data between source databases and destination systems, handling schema changes such as renaming a primary key can pose certain challenges. This article explains the steps and considerations involved in successfully renaming a primary key in the context of database replication using these tools.

Understanding Debezium and Kafka Connect JDBC Sink Connector

Debezium is an open-source distributed platform for change data capture (CDC). It monitors the databases and captures row-level changes, which then can be published to Kafka topics. Debezium represents each row change as a Kafka message, where the message key typically includes the primary key of the row, and the message value includes the row data.

The Kafka Connect JDBC Sink Connector is used to import data from Kafka topics into a relational database. It relies on the message key and value to insert or update records in the database.

Challenge in Renaming Primary Keys

Renaming a primary key in the source database does not automatically propagate to the destination database when using Debezium and Kafka Connect. This process involves coordination between the schema metadata captured and propagated by Debezium and the schema expectations of the JDBC Sink Connector.

Step-by-Step Process for Renaming Primary Key

1. Update Source Database Schema: Begin by updating the primary key in your source database. This involves altering the table schema.

   ALTER TABLE your_table_name RENAME COLUMN old_primary_key TO new_primary_key;

1. Configure Debezium to Handle Schema Changes: Debezium must be configured to handle this schema change effectively. Ensure that Debezium is capturing the DDL changes. This can usually be controlled through the include.schema.changes configuration setting.
2. Management of Kafka Messages: Since Debezium captures the schema changes, the messages in Kafka will now start showing the new primary key name. However, the messages in Kafka topics prior to this change will have the old key.
3. Update Kafka Connect Sink Configuration: Modify the Kafka Connect JDBC Sink Connector configuration to recognize the new primary key name. This might involve changing the pk.fields setting to map to the new primary key name.

   "pk.fields": "new_primary_key"

1. Data Consistency Check: Ensure data consistency between the source and destination databases. Pay attention to how primary key changes might impact the existing data and ongoing transactions.
2. Resuming the Connectors: Restart the connectors to apply these configuration changes. Ensure that there are no synchronization issues or errors in logs.
3. Testing and Validation: Perform thorough testing to validate that the new schema changes with the renamed primary key are consistently replicated from the source to the destination database.

Summary Table

Additional Considerations

• Backward Compatibility: You might need to consider the impact of these changes on systems that consume data from the Kafka topics.
• Data Integrity: Special care should be taken to ensure that data integrity is maintained during the transition period of a primary key rename.
• Performance Impact: Monitor the system for any performance degradations during and after the changes are made.

Handling schema changes such as renaming a primary key requires careful planning and execution within Debezium and Kafka Connect environments. By following the outlined process and considerations, you can ensure that both your source and destination databases are kept in sync with the correct schema relations and minimal disruption.