数据更改后，memcached的行为如何？

Question

通过阅读这个在PHP上使用memcached的简短示例 ，我想知道memcached如何知道何时对数据的请求实际上需要来自数据库而不是来自缓存。

Answer 1

It doesn't, you code does this. In most cases you will do something like this:

key = /* build cache key somehow */
data = memcache.get(key)
if data is null:
  data = /* read data from database */
  cached.set(key, data)

// now you can use the data

Answer 2

It doesn't. It comes down to your caching strategy. That is so with all forms of cache, a tradeoff between getting the latest data and getting some data quickly. If you need to have the data up to date, invalidate (delete) the cache when updating the original. If performance is more important, let the cache expire by itself, at which point it will be renewed. Or something somewhere in-between. It depends on your restrictions and goals.

Answer 3

I think you need to program that logic.

eg When you update the database then update the memcached value associated with that key, or make that key expire.