Cache 基础知识
缓存失效 Cache Invalidation
| 名称 | 释义 | 优点 | 缺点 |
|---|---|---|---|
| Write-through cache | 数据同时写入缓存和数据库中 | <ul><li>保持缓存和数据库的数据一致性</li><li>允许写入后快速读取</li><li>系统故障如断电时不会丢失数据</li></ul> | 写操作的 latency 较高 |
| Write-around cache | 数据绕过缓存直接写入数据库中 | 减轻缓存写的压力 | 读取最近写入的数据时，会发生 cache miss，再从数据库中读，这会产生较高的读延迟 |
| Write-back cache | 数据写入缓存后，一次请求就结束了，返回给客户端。对数据库的写操作会后续再执行（比如满足特定条件或者一段时间后） | 对于写操作密集的应用，带来低延迟和高吞吐量 | 系统故障时可能会丢数据 |
缓存驱逐策略 Cache eviction policies
常见的策略有：
- First In First Out (FIFO): The cache evicts the first block accessed first without any regard to how often or how many times it was accessed before.
- Last In First Out (LIFO): The cache evicts the block accessed most recently first without any regard to how often or how many times it was accessed before.
- Least Recently Used (LRU): Discards the least recently used items first.
- Most Recently Used (MRU): Discards, in contrast to LRU, the most recently used items first.
- Least Frequently Used (LFU): Counts how often an item is needed. Those that are used least often are discarded first.
- Random Replacement (RR): Randomly selects a candidate item and discards it to make space when necessary.
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