After downloading and checking the source code of the MVC Donut Caching project, we have finally found the reason towards why this was happening.
The DonutOutputCache attribute defined in this project makes use of an IKeyBuilder to generate the cache key used to store the output HTML in. The default DevTrends.MvcDonutCaching.KeyBuilder class which comes with the project generates a key which is made up of the following parts:
- Prefix
- Controller Name
- Action Name
- Querystring parameter values (depends on the
CacheSettings.Options having the OutputCacheOptions.IgnoreQueryString flag set on)
- Form parameters (depends on the
CacheSettings.Options having the OutputCacheOptions.IgnoreFormData flag set on)
- Route Values
- If you have
VaryByParam property set to:
none, then all the querystring / form / route values are cleared- If you have it set to anything apart from
*, then it would just consider such parameters only
VaryByCustom parameter would end up calling the same GetVaryByCustomString key generator within the System.Web.HttpApplication.
The above generated key was causing issues for us as a different key was being generated when we weren't aware of such parameters. For this reason, the methods were being called several times as since the website was on the product servers, users, search engines, bots and other requests with different querystring / form / route values where being passed and hence a new key was being generated.
Our solution was to create our own custom IKeyBuilder which was passed on instead of the default IKeyBuilder and solved this issue.