My first impression of AppFabric Cache is that it's essentially a distributed hashtable in the same vein as memcached. The typical usage pattern of such a cache is that there is no guarantee that your data will be in the cache (old entries are evicted to make space for new ones), but with sufficient RAM they usually will be.
On the other hand MS provide a Web Session State Provider that stores session data in an AppFabric Cache. This appears to be a completely different usage pattern as we now require the cached items to never be evicted as a result of memory pressure. To achieve this MS provide a high-availability mode that keeps redundant copies of all data, furthermore eviction can be disabled, which in turn requires us to allocate sufficient RAM to ensure that the cache never reaches capacity.
It seems likely that an application would benefit from using both types/modes of cache, but as far as I can tell AppFabric RAM cannot be ringfenced within a cluster or host, hence the web session state may (and generally will) experience memory pressure in that case. The only solution I can see is to operate two AppFabric Cache clusters, one for each mode.
Is the above a good representation of the situation or am I missing some config setting that addresses this scenario?
