Track · 2:37 · Liner note
Sparse Index Afternoon
A sparse index stores one entry per block of rows rather than one per row, which keeps it tiny while still letting the engine skip most of the data, and ClickHouse uses one for its primary key.
A dense index remembers every row. A sparse one remembers just enough: the first entry of each block, which is often all you need to know whether a block can be skipped. Sparse Index Afternoon is about that economy, the art of leaving out detail and still finding your way.
It also explains why column order in a sort key matters so much. Put the columns you filter on first and the engine can ignore most of the table without reading it. An unhurried afternoon of schema tuning can buy years of speed.