Sql – Clear the cache at a specific time in ASP.NET 2.0

asp.netcachingsqlcachedependency

So I have a process which runs at midnight which sets a start and end point for a flash object. This only needs to run once a day, so I'm obviously caching the result set.

However, the problem I'm running into is, if the data is still cached after midnite, it's not pulling in the most correct data, until the cache expires.

I basically need the cache to expire at 11:59:59PM, so that at 12:00am it gets the correct data.

I'm guessing a SQL Cache Dependency on the table I'm pulling the data from would be ideal, however I have never set that up before.

Is there a way to tell the cache to remove a specific item at exactly midnite?

Thanks guys!

–Absolute Expiration—

I think I got it:

DateTime expireWeights = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 23, 59, 59, 999);
Cache.Insert("CacheItemName", itemToCache, null, expireWeights, System.Web.Caching.Cache.NoSlidingExpiration);

Best Answer

You can set an absoluteExpiration time on the Cache object, which is a DateTime.

You can also combine an absoluteExpiration with a SqlCacheDependency.

Regarding the issue of it not pulling the new data when the cache expires: you can wire up a CacheItemRemovedCallback to receive notification of when it expires, and refresh the cache at that time.

Related Solutions

What’s the best method for forcing cache expiration in ASP.NET

There are many ways to make these caching expire, like page outputcache by

Page.Response.Cache.SetCacheability(HttpCacheability.NoCache)

Time-based dependency simply expires the item at a defined point in time.

Response.Cache.SetExpires(DateTime.Now.AddSeconds(360));
Response.Cache.SetCacheability(HttpCacheability.Private)
Response.Cache.SetSlidingExpiration(true);

Now when it comes to monitoring cache, unless there is an API on the cache to tell you, then there is no direct way.

You could of course enumerate the cache,key-value pairs and then calculate the size of each item stored. Doesnt sound easy right??

So here's to make your cache monitoring easy. Frankly saying i never used it myself, but you can give it a try, just the matter of adding a dll to your application.

And here's something for your cache keys view,

' display contents of the ASP.NET Cache
If Cache.Count > 0 Then    
  cc.Append("<b>Contents of the ASP.NET Cache (" _    
          & Cache.Count.ToString() & " items):</b><br />")    
  For Each item As Object In Cache    
    cc.Append("Key:'" & item.Key & "' Type:" _    
            & item.Value.GetType().ToString() & "<br />")    
  Next    
Else    
  cc.Append("<b>ASP.NET Cache is empty</b>")    
End If

What’s the difference between Cache-Control: max-age=0 and no-cache

I had this same question, and found some info in my searches (your question came up as one of the results). Here's what I determined...

There are two sides to the Cache-Control header. One side is where it can be sent by the web server (aka. "origin server"). The other side is where it can be sent by the browser (aka. "user agent").

When sent by the origin server

I believe max-age=0 simply tells caches (and user agents) the response is stale from the get-go and so they SHOULD revalidate the response (eg. with the If-Not-Modified header) before using a cached copy, whereas, no-cache tells them they MUST revalidate before using a cached copy. From 14.9.1 What is Cacheable:

no-cache

...a cache MUST NOT use the response to satisfy a subsequent request without successful revalidation with the origin server. This allows an origin server to prevent caching even by caches that have been configured to return stale responses to client requests.

In other words, caches may sometimes choose to use a stale response (although I believe they have to then add a Warning header), but no-cache says they're not allowed to use a stale response no matter what. Maybe you'd want the SHOULD-revalidate behavior when baseball stats are generated in a page, but you'd want the MUST-revalidate behavior when you've generated the response to an e-commerce purchase.

Although you're correct in your comment when you say no-cache is not supposed to prevent storage, it might actually be another difference when using no-cache. I came across a page, Cache Control Directives Demystified, that says (I can't vouch for its correctness):

In practice, IE and Firefox have started treating the no-cache directive as if it instructs the browser not to even cache the page. We started observing this behavior about a year ago. We suspect that this change was prompted by the widespread (and incorrect) use of this directive to prevent caching.

...

Notice that of late, "cache-control: no-cache" has also started behaving like the "no-store" directive.

As an aside, it appears to me that Cache-Control: max-age=0, must-revalidate should basically mean the same thing as Cache-Control: no-cache. So maybe that's a way to get the MUST-revalidate behavior of no-cache, while avoiding the apparent migration of no-cache to doing the same thing as no-store (ie. no caching whatsoever)?

When sent by the user agent

I believe shahkalpesh's answer applies to the user agent side. You can also look at 13.2.6 Disambiguating Multiple Responses.

If a user agent sends a request with Cache-Control: max-age=0 (aka. "end-to-end revalidation"), then each cache along the way will revalidate its cache entry (eg. with the If-Not-Modified header) all the way to the origin server. If the reply is then 304 (Not Modified), the cached entity can be used.

On the other hand, sending a request with Cache-Control: no-cache (aka. "end-to-end reload") doesn't revalidate and the server MUST NOT use a cached copy when responding.