Sequin's process for real-time replication of Airtable's API data to Postgres databases faced challenges due to Airtable's limitations, such as difficulty in detecting changes, a flexible schema, and low throughput. Initially, Sequin implemented a "rebuild sync" method, which required reconstructing the entire database with each sync to accommodate schema changes. To improve efficiency, Sequin transitioned to syncing directly to the public schema using upsert statements, reducing lag time and write operations. Further optimization involved in-memory fingerprinting to reduce database read operations, shifting the processing load to workers. This iterative development eventually led to the creation of a proxy that ensures immediate consistency between Airtable writes and subsequent database reads, enhancing the system's reliability and performance.