// LRU iterator for the key and block.
    std::shared_ptr<Block> block = Lookup(key);
    if (!block) {
      std::cerr << "No block for key " << key.first << "@" << key.second;
      abort();
    }
    MaybeFetch(key, block, status);
    if (TF_GetCode(status) != TF_OK) return -1;
    UpdateLRU(key, block, status);
    if (TF_GetCode(status) != TF_OK) return -1;