Polyglot Persistence and Integration Questions

Designing systems that combine multiple database technologies to satisfy diverse data and workload requirements and integrating them reliably. Topics include evaluation criteria for mixing relational databases, document stores, key value stores, time series databases, graph databases, and search engines; change data capture and event driven integration patterns for keeping systems synchronized; patterns for reliable cross system updates such as transactional outbox and idempotent processing; approaches to distributed transactions including two phase commit and saga orchestrations and when to prefer each; data pipeline and stream processing considerations for synchronization and eventual consistency; backup and recovery across heterogeneous systems; monitoring, testing, and schema evolution strategies; and techniques to minimize vendor lock in and operational complexity. Candidates should demonstrate how to reason about consistency boundaries, data ownership, and integration failure modes.