Question

I am using Caching Application Block for caching. I have a few large objects that are cached. The issue is that items are removed from cache because of Scavenging. Now since fetching objects again from database is expensive, I am thinking of using IsolatedStorage to also persist objects on disk. Have the following questions:

1. Say an item A is removed from cache because of scavenging. Will it also be removed from IsolatedStorage ? If it does then what is the purpose of persisting in IsolatedStorage. I wanted to use IsolatedStorage so that even if item is scavenged, it at least can be picked and populated from the storage ?

2. Since the objects are huge, I want to refresh them only once in 24 hours. But the only way to replace them so that there is no affect on end user is to first fetch items and then replace them in cache rather than allow to expire and then start fetching data ?

Answer 1

1. Yes, it will also get removed from IsolatedStorage. Basically, all actions get funneled both to the in-memory cache and IsolatedStorage. The purpose is to have persistence after the application closes. Anything that was still in the cache (and not scavenged) is persisted to disk and can be restored to the in-memory cache the next time the application runs.
2. I’m guessing this is the ol’ “do database operations on a separate thread” issue. I’ve used the CAP before and had this problem in a WinForms app. You’ll probably want to write your own custom cache manager or something, which EntLib supports nicely. From it you could manage scavenging directly and also implement BackgroundWorkers or Tasks or something when it comes time to re-fetch data. Probably other ways you could handle it, but that would keep it contained in the cache manager. Otherwise, you’ll have to have something else in the app monitor the cache and refresh it as necessary.