Question

I have a really strange problem and I’m completely puzzled.

I have a piece of code that parses some data and stores the result in our webserver’s HttpRuntime.Cache using the Insert method. This is stored for 10 seconds. There seem to be some problems so I created a test page that retrieves a simple object from the cache and displays if it is null or not. To add the object to the cache, I use:

HttpRuntime.Cache.Insert(CHECK_KEY, new object(), null, DateTime.Now.AddSeconds(10), System.Web.Caching.Cache.NoSlidingExpiration);

In a test page, I try to retrieve the object:

var isInCache = this.cacheService.Get<object>(CHECK_KEY) != null;

and the method of the cacheService is:

public T Get<T>(string key)
{
  return (T)HttpRuntime.Cache.Get(key);
}

Now the strange part. If I call a URL that calls the ‘Insert’ method, and go to my test page to retrieve it, the value of isInCache is false in about 99% of the time. Sometimes it works correctly for the whole 10 seconds (e.g. I refresh my test page every second and I get true 10 times) but again, most of the time it just returns false.
Now, when I keep F5 pressed, I sometimes see true in my output, in the blink of an eye, which means that the key CAN be found! This is not some browser cache, because it will only flash true intermittetly for the 10 seconds of cache duration, after which is it will only display false (which is logical, since the key is expired). So my question is:

• WHY will retrieving a simple object from the cache fail most of the time?
• There are other items in the cache (on the same test page) that do get retrieved, just not that object.

To make things worse, this (of course!) works flawlessly on my local machine, on the test machine, just not production. I’m pretty clueless. Please help 🙂

EDIT:
Ok so I’m now testing in two different browsers, IE9 and Chrome… and IE9 is correctly showing the items in the HttpRuntime.Cache but Chrome is NOT. It shows always false and no other cached data, except when keeping F5 pressed it will occassionally show it. Since when is HttpRuntime.Cache browser dependant???
Extra edit: IE9 shows no more cached data. So while it can differ across browsers, it’s not that IE will always work and chrome not… it differs.

EDIT2:
So I’m passing the variables to my view using ViewData:

ViewData["machineName"] = machineName;
ViewData["isInCache"] = isInCache;
ViewData["A"] = A;
ViewData["B"] = B;

Machinename comes from Server.MachineName, isInCache is the object, variable A is not from the HttpRuntime.Cache, variable B does, which is also intermittently not present.

Answer 1

After much debugging and thought, it appeared that the hosting provider had the ‘Maximum Worker Processes’ in IIS 7 Application pool settings to a value larger than 1. The HttpRuntime.Cache is not shared in a web farm, thus it could well be that I hit the ‘wrong’ instance which did not have the object cached. Continuously pressing F5 would have me occassionaly hit the instance which did have the value cached.