Does CitusDb fit in olap analytical workloads to do aggregations on hundreds millions of records using varying order and size of dimensions (eg druid) in max of 3 seconds response time using as few boxes as possible - Or there are other techniques have to be used along with Citusdb? Can you shed a light on your experience with CloudFlare in terms of cluster size and queries perf?
Hundreds of millions of records in <=3 seconds is not really a big challenge with a good data model and proper indexing on even a single server.
I work for a BI consultancy and we don't even bat an eye until we hit billions of records in a primary fact table.
Certainly the DB server does need to scale vertically to some extent as you pass through the orders of magnitude > 10M. A good columnstore engine is also worthwhile to consider.
