YugabyteDB, a distributed SQL database, has been using Postgres 11 since its inception and is now upgrading to Postgres 15, a newer version of the PostgreSQL database management system. The upgrade is necessary due to the discontinuation of support for Postgres 11 by the core development team. YugabyteDB's initial approach was to build its own SQL engine from scratch, but it soon realized that implementing all the features of Postgres would be too complex and time-consuming. Instead, they integrated the Postgres query layer with their existing distributed database, making it a Postgres-compatible system. The upgrade is part of a series of efforts to deliver a newer version of Postgres to users while maintaining compatibility with existing applications. YugabyteDB's architecture combines the reliability and scalability of Postgres with its own distributed storage and transaction layer, allowing for fault tolerance and horizontal scalability. The company has been working on updating the Postgres version for some time, and they aim to deliver a highly reliable, scalable, available, and secure system for users' distributed Postgres needs. The upgrade process is complex due to the large amount of code changes required, but YugabyteDB is committed to ensuring that the new version meets their high standards.