docs: function setKey(key, val, flag, expiry, xflag, req) {
    var exists = this._data[key] !== undefined;
    var o = {v: val, t: Date.now()};
    if((xflag === Constants.NX && exists)
      || (xflag === Constants.XX && !exists)) {
      return undefined;
    }
    this._data[key] = o;
    if(!exists) {
      this._keys.push(key);
    }
    if((flag === Constants.EX || flag === Constants.PX)
      && expiry !== undefined) {
      expiry = flag === Constants.EX
        ? Date.now() + (expiry * 1000)
        : Date.now() + expiry;
      this.setExpiry(key, expiry, req);
    }
    return Constants.OK;
  }