Honestly you don't even need some kind of fancy google architecture, query engine, or columnar data store. I recently implemented 99% of what mixpanel provides

Honestly you don't even need some kind of fancy google architecture, query engine, or columnar data store. I recently implemented 99% of what mixpanel provides using S3 and lambda. I stored the events on S3 (actually get requests to an S3 bucket with logging turned on and what I wanted to track seeialized as JSON in the query string of the request. From here it's as easy as writing lambda functions to process the logs and output the results in some location where a static web app can visualize them.