Is Caching in C# the right approach for me?

Question

I've tried to read up on Caching in ASP.NET and still have a few questions.

1. When using a Sql Cache Dependency ... I know that you can specify which tables will be monitored but if a change happens to any one of those tables does it reset the entire cache? I understand that I don't want to cache tables that will have frequent changes but we could end up with a good handful of cached tables and even if each table only gets a few updates a day, that could turn into 50ish resets of the cache daily (8 hour window).

2. I would be creating and maintaining this cache via a GAC DLL. A large number of different applications would be accessing that GAC at any one time. Does each application maintain its own copy of the cache or is it just stored in one global location (or possibly per app pool)?

3. Is there a physical location on the server where I can see how much space the Cache is currently consuming? This would be extremely pertinent if each application maintains its own Cache as that could end up taking large amounts of disk space.

4. Is there some way to physically force the cache to rebuild itself? I could see my boss assuming that the cache was at fault for a particular issue and I'd need to be able to rule that out at the rootest level. No "changing a record and saying that SHOULD rebuild the cache" but rather "doing [Action X] and KNOWING that whatever was in the cache is now gone"

Thanks in advance for your answers and time.

Answer 1

1. SqlCacheDependency only monitors tables in the old-style SQL 2000 approach, which relies on triggers and polling. The SQL 2005+ method monitors changes at the row level, and uses Service Broker. At the level of the Cache object, changes will invalidate just the Cache entries associated with the given SqlCacheDependency (not the entire cache).

2. Each application has a separate copy of the Cache. If you have many apps sharing the same data, you might consider creating a separate "caching server," and have your apps get their data from there, using WCF -- basically add another tier to your app.

3. You can look at a couple of cache-related performance counters, but if your concern is disk space, then there's nothing to worry about, since the ASP.NET cache is stored entirely in RAM. In addition, if RAM gets too full, one feature of the cache is that it will let go of old/infrequently referenced objects to make room for new objects.

4. The easiest way to force the cache to be dropped is to simply recycle your application or AppPool (which happens once a day or so by default anyway). If you want something more targeted, you would need to write some code to forcibly remove certain items from the cache, either using Cache.Remove() or using linked dependencies.

Answer 2

from top of my head:

1. Only that table's content will be invalidated.
2. Each web application has it's own cache.
3. Cache is stored in memory. and see this question How to determine total size of ASP.Net cache? regarding cache size
4. http://bit.ly/vsqNDl this may help