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Isn’t there also hash based index for random keys?

• benwilber0 2y ago
  Maybe? idk. Not in Postgres. The default index is a B-Tree. A hash-based index would be terrible for disk-seeking, in any case.
  • eurleif 2y ago
    https://www.postgresql.org/docs/current/indexes-types.html#INDEXES-TYPES-HASH https://www.postgresql.org/docs/current/indexes-types.html#I...
    • benwilber0 2y ago
      Probably the worst PK index of all time. There's a reason why it's barely ever used.
    • paperplatter 2y ago
      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.