I think you might be asking the wrong questions. They key questions are Queries per second and the median response size of the query.
For example at reddit (15 years ago) we had 10x more vote traffic than comment traffic, but we only needed two databases to handle votes (technically only one the other was just for redundancy).
But we needed nine comments databases. Mainly because the median query response was so much bigger for comments.
For example at reddit (15 years ago) we had 10x more vote traffic than comment traffic, but we only needed two databases to handle votes (technically only one the other was just for redundancy).
But we needed nine comments databases. Mainly because the median query response was so much bigger for comments.