It's common to see here that Postgres hosted in RDS can handle 99% of workloads up to millions of users. I'm building an IoT app with a plan to ingest the IoT traffic into dynamo partitioned on user id (I'm quite familiar with the tradeoffs) and everything else be in Postgres. A few services but not microservice (basically: core service, identity service, IoT data service, notification service). Ingesting and monitoring about 1,000,000 IoT devices daily (1 packer per device per day) and about 1,000,000 users with only 5,000 active users per day (basically we monitor user IoT devices 24/7 but only some 5,000 users will have anomalous results and log in).

In the database posts & discussions here I sometimes find that the opinions are strong but the numbers are missing. Obviously applications have wide variation in traffic and query complexity so apples to apples comparisons are hard. Still, I would greatly benefit from hearing some real world experiences with numbers.

Rough approximation database questions for current or prior applications:

1. How many customers do you have?

2. What's expected daily traffic? Peak traffic?

3. What database engine or engines do you use?

4. How many rows or how much storage does your db have?

5. What else about your application is relevant for database load?

6. Microservice, Service, or monolith. Happy with it?