ClickHouse Evaluates IN with Hash Sets
IN is not a comparison, it is a hash set. ClickHouse picks one of thirteen specialisations based on the shape of the right-hand side, packs integer keys into the hash…
Set
CPython's set and frozenset Implementation in C: One Hash Table, Two Flavors
CPython’s set is an open-addressing hash table with three slot states — unused, dummy, active — and dummies are what keep deleted keys from breaking probe chains.