Dotnet Core In Memory Cache - what is the default expiration

Question

I'm using MemoryCache in a dotnet core C# project. I'm using it store a list of enums that I read out of a collection (I want to store it since it uses reflection to load the enums which takes time).

However, since my collection isn't going to change, I don't want it to expire at all. How do I do that? If I don't set any Expiration (SlidingExpiration or Absolute Expiration), will my cache never expire?

Answer 1

If you do not specify an absolute and/or sliding expiration, then the item will theoretically remain cached indefinitely. In practical terms, persistence is dependent on two factors:

1. Memory pressure. If the system is resource-constrained, and a running app needs additional memory, cached items are eligible to be removed from memory to free up RAM. You can however disable this by setting the cache priority for the entry to CacheItemPriority.NeverRemove.

2. Memory cache is process-bound. That means if you restart the server or your application restarts for whatever reason, anything stored in memory cache is gone. Additionally, this means that in web farm scenarios, each instance of your application will have it's own memory cache, since each is a separate process (even if you're simply running multiple instances on the same server).

If you care about only truly doing the operation once, and persisting the result past app shutdown and even across multiple instances of your app, you need to employ distributed caching with a backing store like SQL Server or Redis.