Explaining a ClickHouse read

What happens

A count of three million ClickHouse events by kind is explained with a filter on user_id, the second column of the sorting key, and the plan reads 368 of 371 granules; one line is changed to a day of event_time, and the plan now reads 1 of 11 parts and 3 granules.

Chapters

1. 0:00 Three million events in ClickHouse
2. 0:04 Count them by kind for one user
3. 0:18 Explain it: the key cannot skip much
4. 0:27 Filter on the first column of the key instead
5. 0:38 One part, a few granules