[pas]

the right way to look at it - IMHO - is to interpret "lots of RDS experience" as complete lack of run-your-own postgreSQL experience. and given that it's not surprising that their cost-benefit math give them the answer of "invest into a custom middleware, instead of moving to running our postgreSQL plus some sharding thing on top"

of course it's not cheap, but probably they are deep into the AWS money pit anyway (so running Citus/whatever would be similar TCO)

and it's okay, AWS is expensive for a lot of bootstrapped startups with huge infra requirements for each additional user, but Figma and Notion are virtually on the exact opposite of that spectrum

also it shows that there's no trivial solution in this space, sharding SQL DBs is very hard in general, and the extant solutions have sharp edges