Which Side Is Small Enough

Concepts covered: paBroadcastJoin

The broadcast trade is network for memory: you avoid shuffling the big table by making every executor hold the entire small one. So the operative question about the small side is not how many rows it has but whether a full copy sits comfortably in one executor's memory next to everything else that executor is doing: shuffle buffers, cached data, the tasks themselves. If the answer is comfortably yes, on every executor, with room to spare after the hash-map form inflates it, broadcast is on the table. If you have to squint, it is not. The reliable instinct is to think in categories of tables, not bytes. Lookup and dimension tables describe a bounded world: countries, currencies, product catalogs, store locations, status codes. They are small because reality is small, and they grow slowly if

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