Keydb Eng: Updated

In the words of its creators: "KeyDB is what you’d get if you took Redis and made it fast on modern hardware." For many, that’s exactly what they need.

// Callback executed by background thread when data is ready void onTieringFetchComplete(client *c, robj *value) // 1. Restore value to the main hash table in RAM dbAdd(c->db, c->key, value); keydb eng