How do you synchronize data across systems?

Data synchronization across systems typically involves establishing processes that ensure consistent data states between multiple databases, applications, or services. The core approach revolves around identifying changes in a source system, transmitting those changes to target systems, and applying them reliably. Common methods include batch processing (scheduled data transfers), event-driven updates (triggered by changes), or hybrid approaches. For example, a retail application might synchronize inventory data between a central database and regional servers nightly via batch jobs, while real-time order updates could use event-driven messaging to keep systems in sync immediately.

Specific synchronization techniques depend on system requirements. For transactional consistency, tools like database replication or distributed transactions ensure atomic updates across systems. When eventual consistency is acceptable, event sourcing or log-based replication (e.g., using change data capture) can propagate changes asynchronously. Conflict resolution strategies like last-write-wins, manual intervention, or application-specific merge logic are critical for handling concurrent updates. A practical example is using a message broker like Apache Kafka to stream order status changes from a payment service to a shipping system, with timestamps resolving conflicts if the same order is updated simultaneously in both systems.

Key challenges include handling network failures, schema mismatches, and performance optimization. Implementing idempotent operations (to avoid duplicate updates) and retries with backoff strategies helps maintain reliability. Schema validation tools like JSON Schema or Protobuf can enforce data compatibility during transfers. Monitoring synchronization latency and implementing data checksums help detect drift. For instance, a healthcare application might use database triggers to capture patient record changes, serialize them as Avro messages, validate them against a schema registry, and queue them for processing in an analytics system, with dead-letter queues handling failed sync attempts.