Question

I would like to use output caching with WCF Data Services and although there’s nothing specifically built in to support caching, there is an OnStartProcessingRequest method that allows me to hook in and set the cacheability of the request using normal ASP.NET mechanisms.

But I am worried about the worker process getting recycled due to excessive memory consumption if large responses are cached. Is there a way to specify an upper limit for the ASP.NET output cache so that if this limit is exceeded, items in the cache will be discarded?

I’ve seen the caching configuration settings but I get the impression from the documentation that this is for explicit caching via the Cache object since there is a separate outputCacheSettings which has no memory-related attributes.

Here’s a code snippet from Scott Hanselman’s post that shows how I’m setting the cacheability of the request.

protected override void OnStartProcessingRequest(ProcessRequestArgs args)
{
    base.OnStartProcessingRequest(args);
    //Cache for a minute based on querystring
    HttpContext context = HttpContext.Current;
    HttpCachePolicy c = HttpContext.Current.Response.Cache;
    c.SetCacheability(HttpCacheability.ServerAndPrivate);
    c.SetExpires(HttpContext.Current.Timestamp.AddSeconds(60));
    c.VaryByHeaders["Accept"] = true;
    c.VaryByHeaders["Accept-Charset"] = true;
    c.VaryByHeaders["Accept-Encoding"] = true;
    c.VaryByParams["*"] = true;
}

Answer 1

Ahh! I feel dumb now… It appears I can set this limit in IIS’s configuration, which makes sense since I guess IIS is providing the output caching services to ASP.NET in the first place.

And as an added bonus it seems IIS has already defaulted to some reasonable settings for this:

Maximum cached response size (in bytes) Specifies the maximum size of
a cached response for both the
user-mode and kernel-mode caches. The
default value is 262144 bytes. This
field is enabled at the server level
only; it is read-only at all other
levels.

Cache size limit (in MB) Configures the size limit of both the
user-mode and kernel-mode caches. You
can type a size (in MB) or type 0. If
you type 0, IIS uses half of the
available physical memory or virtual
memory, whichever is less. This field
is enabled at the server level only;
it is read-only at all other levels.