Heap uses Citus DB which is not RDS compatible https://www.citusdata.com/customers/heap

Citus has been a huge part of our scaling story from RDS (maxed out instances and did a ton of tuning) to Citus Cloud. I can only imagine that Heap has a ton more problems than we've experienced.

Heap’s usage of Citus predates the rollout of Citus Cloud so definitely hats off to them for their operational know-how. I wonder if they’ve considered switching — my guess is that the compressed filesystem probably results in material savings for them so that’s likely a reason to keep operating their own cluster.

It does probably make sense for heap to manage it themselves given it is a core competency of theirs, based on their indexing talks