A query joins a 2-billion-row fact table to a 40,000-row dimension table. The optimizer has to decide which side to broadcast and which side to hash. It reads the manifests and finds row counts, min and max values, and null counts for every column in every file.
Source: [Dev.to](https://dev.to/alexmercedcoder/inside-the-puffin-file-format-p21)