AP 的应用场景：表现为订单创建后，立即返回短信发送成功，无需等待短信是否发送成功，保证用户体验。但是 AP 有很大的问题，例如爆了一件神话装备，但是服务器宕机了，缓存没有写入磁盘，导致装备丢失。
BASE 最终一致性
AP 缺乏数据一致性的解决方案：BASE，是对 CAP 的补充，让短信尽可能地发送成功
Basically available: reading and writing operations are available as much as possible (using all nodes of a database cluster), but may not be consistent (the write may not persist after conflicts are reconciled, the read may not get the latest write)
基本可用，就是基本实现用户的基本价值和诉求，创建订单后立即返回，就是基本可用的体现
Soft-state: without consistency guarantees, after some amount of time, we only have some probability of knowing the state, since it may not yet have converged
Eventually consistent: If we execute some writes and then the system functions long enough, we can know the state of the data; any further reads of that data item will return the same value
最终一致性，表示通过技术手段，过一段时间后，让数据保持一致性。最终一致性只是对 AP 打补丁，不能 100% 实现 Consistency。