If data is requested and is in the cache (a phenomenon called a cache hit), the data is retrieved from the cache, avoiding having to retrieve it from memory or disk.

• 如果数据被请求，并且数据在高速缓存区（这种情况就是高速缓存区命中），就直接从高速缓存区读取，而不需要从内存或者磁盘读取。