Question

Our application adds objects to the cache using the following

int cacheTimeout = 5; // Default 5 minute timeout
if(ConfigurationManager.AppSettings["CacheTimeout"] != null)
{
    cacheTimeout = Convert.ToInt32(ConfigurationManager.AppSettings["CacheTimeout"].ToString());
}
_cache.Insert(Key, CacheItem, null, DateTime.MaxValue, new TimeSpan(0, cacheTimeout, 0));

Our manager is concerned about possible caching issues and wants to know, what happens if you insert an object with a 0 length time span.

I think the object will be immediately deleted. Right or wrong?

Answer 1

Answer is “Wrong”.

When inserted into the cache with the absolute expiration set to NoAbsoluteExpiration and the sliding expiration set to new TimeSpan(0,0,0), the callback is not fired immediately. I didn’t wait to see when it would fire, if ever – maybe it’s 20 minutes, maybe it’s never.

So changed the code to this:

int cacheTimeout = 5; // Default 5 minute timeout
if(ConfigurationManager.AppSettings["CacheTimeout"] != null)
{
    cacheTimeout = Convert.ToInt32(ConfigurationManager.AppSettings["CacheTimeout"].ToString());
}
TimeSpan expiration = cacheTimeout > 0 ? new TimeSpan(0,cacheTimeout,0) : new TimeSpan(0,0,1);
_cache.Insert(Key, CacheItem, null, System.Web.Caching.Cache.NoAbsoluteExpiration, expiration, CacheItemPriority.Default, OnUpdateCallback);

That way if we do have caching problems we can update web.config to set the cache time out to 0 and have a 1 second expiration.