How do you use CDC tools for database sync?

To use CDC (Change Data Capture) tools for database synchronization, you start by configuring the tool to monitor and capture changes in the source database. CDC works by tracking insert, update, and delete operations, often using database transaction logs, and streaming these changes to a target system. Tools like Debezium, AWS Database Migration Service (DMS), or SQL Server Change Data Capture can be configured to listen for these events. For example, Debezium connects to databases like PostgreSQL or MySQL, reads their transaction logs (e.g., WAL in PostgreSQL or binlog in MySQL), and converts changes into events in a format like Avro or JSON. These events are then published to a messaging system such as Apache Kafka, allowing downstream systems to consume and apply them to the target database.

The setup process typically involves enabling CDC features on the source database and configuring connectors. In PostgreSQL, you might enable logical replication and create a replication slot for Debezium. For AWS DMS, you create a replication instance, define source and target endpoints, and configure a task to map tables and manage replication. A critical step is ensuring the CDC tool has access to transaction logs and sufficient permissions to read them. Once configured, the tool captures changes in real time or near-real time, reducing latency compared to batch-based sync methods. For instance, a Debezium connector for MySQL might emit an event like {"op": "u", "before": {"id": 1, "name": "Alice"}, "after": {"id": 1, "name": "Bob"}} for an update operation, which a consumer application can apply to the target database.

When implementing CDC, consider consistency, error handling, and schema differences. Tools like Kafka Connect with Debezium allow transformations (e.g., filtering or renaming fields) to align source and target schemas. For example, if the target database uses a different column name, you can apply a Single Message Transformation (SMT) to modify the event structure. Monitoring is also essential: track lag metrics to ensure changes propagate efficiently and set up alerts for failed events. For high-volume systems, optimize by batching events or using idempotent writes to avoid duplicates. Testing is crucial—validate edge cases like schema changes or large transactions to ensure the sync remains reliable. CDC tools streamline synchronization but require careful tuning to handle real-world complexities.