Multi level cache - Appfabric with MemoryCahe

Question

In my current setup I have a dedicated Appfabric server. Most of the objects stored there are reference objects which means most of the operations are 'Get' operations. Therefore I've considered using LocalCache. Unfortunately, recently I experienced problems with the availability of the cache server resulting from various network issues. The application server continues to work directly with the DB in these cases thanks to a provider I've written. However, it has a very large impact on performance as expected.

I want to be able to use some kind of a local cache for the highly referenced objects, even when the cache server is down. For this purpose I've considered using the MemoryCache of .Net 4. I don't really care about the objects being stale and I rely on a timeout eviction policy, therefore I don't worry about synchronization between the application servers.

I wanted to hear what do you think about this solution. - Are there any other points I should consider? - Is there a better solution to provide fast access for highly referenced objects even when the cache server is down?

Answer 1

Did you consider AppFabric's local cache feature? Or is it not suitable for you?

Answer 2

Appfabric's LocalCache is a client cache, local and inproc to the client application, which stores references of frequently used data, so application does not need to deserialize same object again. However since LocalCache works with the cache server, it would not work if cache server is down.

One solution possible to your problem is as you have mentioned, having an independant client cache so even if cache server goes down, client cache will still be available.

When relying on inproc cache you will have to keep it in mind that in-process caches store reference of cached objects. If your application modifies object after getting from cache, it will be modified in cache as well. Also if multiple threads may end up modifying same item in cache, you will need thread synchronization for such objetcs.

However even using an independant client cache, you application may end up hitting the database frequently, since data in client cache of one application server will not be accessable to other servers.

A better solution might be using replicated cache servers, where each server will have all cached data. This will not only improve get performace for referential data but also will eliminate single point of failure, like in your case.

If Appfabric is not a hard requirement for application, you may look into NCache for better scalability and high availablility.