What is Citus?

  * Open-source PostgreSQL extension (not a fork)
  * Scalable across multiple hosts through sharding and replication
  * Distributed engine for query parallelization
  * Highly available in the face of host failures

Citus horizontally scales PostgreSQL across commodity servers using
sharding and replication. Its query engine parallelizes incoming SQL
queries across these servers to enable real-time responses on large
datasets.
