为什么我应该只在应用程序生命周期的早期创建MemoryCache？

Question

As per MSDN documentation here :

Do not create MemoryCache instances unless it is required. If you create cache instances in client and Web applications, the MemoryCache instances should be created early in the application life cycle. You must create only the number of cache instances that will be used in your application, and store references to the cache instances in variables that can be accessed globally. For example, in ASP.NET applications, you can store the references in application state. If you create only a single cache instance in your application, use the default cache and get a reference to it from the Default property when you need to access the cache.

It doesn't quite explain the reasoning behind this and several other questions have asked about clearing a MemoryCache , but seems to have not reached a solid conclusion. As I have gathered, my options are either to dispose the MemoryCache and create a new instance, which is not advised according to the above documentation, or use the enumerator, which is also not advised due to performance issues. Trim() has been shown to be unreliable, so I'm investigating why instantiating a MemoryCache in the middle of my application lifecycle is considered a bad idea.

To dive into a bit of why I'm curious, the main issue at hand here is that I want my MemoryCache to work only for the scope of a series of method calls. These method calls are made across different instances of the same object, which share data retrieved through the database that, although very unlikely, may change in the short span of a few seconds that I've assigned to the expiration window. My idea was to create a new MemoryCache instance whenever I start off the series of method calls to ensure that I have the most recent data while not hitting the database a high number of times for each of those instances. However, MSDN advises against creating new instances as well and suggests to have all instances in global variables.

So in short, why is it recommended to instantiate a MemoryCache during the beginning of the application lifecycle and why should I have a global reference to MemoryCache s that I use?

Answer 1

Because it wants contiguous memory. You want to do it before memory get fragmented.

I don't know about the global.