A deep dive into hash tables, part 1
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We all know the Hash Match operator. It joins or aggregates data, based on a hash table. That hash table is ideally stored in memory. But if the granted memory is insufficient, then Hash Match will spill to tempdb, which is slow. I assume that every reader of this blog knows this already. But what you probably don’t know is how that hash table is structured. How is the data stored? Where are new rows added, how is the table accessed? To be fair, none of this is useful knowledge, unless you work for the engine team at Microsoft. And…
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