Need to track feature usage for 50k+ users daily

Hi,

I need to track feature usage for an application so I can do the following:

• track feature usage for a user. We have 20+ features and we want to limit feature usage. Think, select count(*) from db where user_id = 1 and feature_id = 1 that have to be calculated on the fly.
• must have fast read write ops.
• able to do machine learning on data
• do I need horizontal scaling?

I've been pointed towards elastic search and wondering if there's better alternatives.