Postgres has it, but it didn't used to, and it's still got caveats.
Beyond Postgres, indexing random values is fundamentally harder than indexing sorted ones, whether you've got a hashmap or btree or something else. The often-cited O(1) lookup complexity of a hashmap assumes everything easily fits in uniform-access memory.
Beyond Postgres, indexing random values is fundamentally harder than indexing sorted ones, whether you've got a hashmap or btree or something else. The often-cited O(1) lookup complexity of a hashmap assumes everything easily fits in uniform-access memory.