When building a durable workflows library, a significant decision was selecting the appropriate data store for workflow metadata, ultimately choosing Postgres due to its technical advantages. Postgres's features such as concurrency control, relational data model, and transaction capabilities make it suitable for scalable and performant workflow systems. Its concurrency control, particularly locking clauses, helps manage distributed queues by reducing contention among workers. The relational model, combined with secondary indexes, supports efficient observability queries over workflow metadata, allowing users to monitor and analyze workflows effectively. Moreover, Postgres enables exactly-once execution guarantees for steps performing database operations by leveraging transactions, ensuring that each step either fully completes or rolls back without re-execution, thereby enhancing the robustness of durable workflows.