Craig Kerstiens covers a misunderstood extension:
Citus is in a small class of the most advanced Postgres extensions that exist. While there are many Postgres extensions out there, few have as many hooks into Postgres or change the storage and query behavior in such a dramatic way. Most that come to Citus have very wrong assumptions. Citus turns Postgres into a sharded, distributed, horizontally scalable database (that’s a mouthful), but it does so for very specific purposes.
Read on to learn when Citus can work well, when it isn’t a good fit, and a few architecture and design recommendations around using the extension.