Citus runs on standard, unpatched PostgreSQL servers. The only modification is installing the extensions into the server. This is a unique and extremely important advantage: most clustered databases that are derived from another database inevitably lag behind and get stuck on an old version of the original database, unable to keep up with the grueling workload of constantly refactoring to build on new releases. Not so for Citus, which doesn’t fork Postgres—it extends it with Postgres’s own extension mechanisms. This means that Citus is positioned to continue innovating on its own software, while continuing to benefit from the strong progress that the PostgreSQL community is delivering on a regular cadence too.
Sharding a multi-tenant app with Postgres
Co-locating data within the same physical instance avoids sending data over the network during joins. This can result in much faster operations. With Citus there are a number of ways to move your data around so you can join and query it in a flexible manner, but for this class of multi-tenant SaaS apps it’s simple if you can ensure data ends up on the shard.