ShardedKV.disel

msg := Put(k,v) | Get(k) | Resp(v_old)

Server: 
  main():
    db = {}
    while m = recv():
      v0 = db[m.k]
      if m is Put: 
        db[m.k] = m.v
      send Resp(v0) to m.src

Client:
  get(k):
    s = hash(k)
    send Get(k) to s
    Resp(v0) = recv()
    return v0

  put(k,v):
    s = hash(k)
    send Put(k,v) to s
    Resp(v0) = recv()
    return v0