The query layer: making big data feel small

How to make dashboard queries over billions of rows fast and affordable: choosing among warehouses, real-time OLAP, lake engines and embedded engines, why queries are slow, partitioning and clustering, when to pre-aggregate and how to route to rollups, materialized views, multi-layer caching with TTLs by freshness, multi-tenant isolation and quotas, a production query service, and the cost mistakes to avoid.