ClickHouse: what is behind the fastest columnar database. Or how to make it click!

A columnar database ClickHouse is in many ways exceptional - it is exceptionally fast, exceptionally efficient, but also, exceptionally confusing. It's approach to handling data goes against principles we use in other databases: its primary index doesn't index each row and doesn't guarantee uniqueness; a secondary index doesn't point to specific rows; JOIN to be avoided and transactions do not exist. But if used correctly, ClickHouse is a superb solution for online analytical processing. The goal of this talk is to help you get the most of ClickHouse and avoid pitfalls. We'll talk about analytics, columnar databases and sparse indexing. We'll look at the most puzzling concepts of ClickHouse, so that by the end of the talk you find them not only logical, but maybe even fascinating.