Why did I do a full scan? Because I wanted to see just how bad it was, and I wanted to see roughly what was in the database. I ran: `select count (distinct fo

Why did I do a full scan? Because I wanted to see just how bad it was, and I wanted to see roughly what was in the database. I ran: `select count (distinct foo)` and got ~9000 distinct items over 2B rows in 12 hours. Running the same query in Clickhouse was O(minute) As a little extra comparison, the total size of the Clickhouse database is 1/2 the size of the indexes in Postgres.