An Aggregate Is a Function, Not a Sum
Summary
The article argues that aggregates can be treated as functions of their underlying documents rather than running sums, addressing duplicates, late arrivals, and outages in streaming workloads using a cell-based recomputation design in ClickHouse. It describes narrow tables, a dirty-cell journal, and ReplacingMergeTree to enable recomputation and scalable, correct reports without double counting.