缓存系统如何在php生命周期中有效？

Question

I'm a little confused here.

I know that for every PHP request, the entire application is bootstrapped all over again.

Given this, how can a cache be effective, if all of the globals are reloaded for each and every request?

For example:

User calls URI/user/view/123. User 123 is loaded from a database and stored in $user.

Why would you cache the contents of $user - when you merely need to refer to the variable in order to get the contents?

Am I missing the point?

Thank you,

Answer 1

Its more like caching images, common database querys

For instance say your site has a lot of articles and each article has categories. And say you dont change categories very often, then using a cached result of a query of the categories table is preferable then doing the query. this is a simplified example.

Another example is with images, if your site needs like thumbnailed version of user photos that they have uploaded instead of having php use the GD library to rescale the image and etc just save a version of that thumbnail version and use it instead of running through the GD code again.

Answer 2

As always, an image is worth a thousand words, here it is :)

( source )

As you can see, you reload some PHP librairies (like the basic environment (Globals, Requests, Cookies, etc), but not everything (in this case, Security, Application, various libraries, Views).

You skip what can be cached ;)