Donut Cache examples from Umbraco UK Festival talk "The need for speed"

DefaultController.cs

public class DefaultController : RenderMvcController
{
	[UmbracoDonutOutputCache(CacheProfile = "LongPageCache",
	Options = OutputCacheOptions.NoCacheLookupForPosts &
	OutputCacheOptions.ReplaceDonutsInChildActions, Order = 100)]
	public override ActionResult Index(RenderModel model)
	{
		return base.Index(model);
	}
}

Global.cs

public class Global : UmbracoApplication
{
	public override string GetVaryByCustomString(HttpContext context, string custom)
	{
		var result = base.GetVaryByCustomString(context, custom);
		if (string.IsNullOrEmpty(custom))
		{
			return result;
		}
		if (UmbracoContext.Current.IsFrontEndUmbracoRequest)
		{
			var keys = custom.Split(new[] { ";" }).ToList();
			if (keys.Contains("url"))
			{
				result += $"pageid={UmbracoContext.Current.PageId};";
				result += $"url={context.Request.Url}";
			}
		}
		return result;
	}
  }

UmbracoDonutOutputCacheAttribute.cs

public class UmbracoDonutOutputCacheAttribute : DonutOutputCacheAttribute
{
    
	public override void OnActionExecuting(ActionExecutingContext filterContext)
	{
        // overrides donut output cache attribute to not cache when in umbraco preview mode or Doctype grid editor preview
		this.Duration = -1;
		var previewMode = UmbracoContext.Current.InPreviewMode;
		if (!previewMode)
		{
			if (UmbracoContext.Current.HttpContext.Request.QueryString["dtgePreview"] == "1")
			{
				previewMode = true;
			}
		}
		if (previewMode)
		{
			this.Duration = 0;
		}
		base.OnActionExecuting(filterContext);
	}
}

UmbracoStartup.cs

public class UmbracoStartup : ApplicationEventHandler
{
	protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication,
		ApplicationContext applicationContext)
	{
		DefaultRenderMvcControllerResolver.Current.
			SetDefaultControllerType(typeof(DefaultController));
      
      PageCacheRefresher.CacheUpdated += this.PageCacheRefresherCacheUpdated;

	}
  
  private void PageCacheRefresherCacheUpdated(PageCacheRefresher sender, CacheRefresherEventArgs e)
	{
		switch (e.MessageType)
		{
			case MessageType.RefreshById:
			case MessageType.RemoveById:
				var contentId = (int)e.MessageObject;
				var doctype = string.Empty;
				var item = UmbracoContext.Current.ContentCache.GetById(contentId);
				if (item != null)
				{
					doctype = item.DocumentTypeAlias;
				}
				this.ClearPageOutputCache(contentId, doctype);
				break;
			case MessageType.RefreshByInstance:
			case MessageType.RemoveByInstance:
				var content = e.MessageObject as IContent;
				if (content == null)
				{
					return;
				}
				this.ClearPageOutputCache(content.Id, content.ContentType.Alias);
				break;
		}
	}
    
    private void ClearPageOutputCache(int contentId, string doctype)
	{
		var enumerableCache = OutputCache.Instance as IEnumerable<KeyValuePair<string, object>>;

		if (enumerableCache == null)
		{
			return;
		}

		// get all output cache keys that contain current page id
		var keysToDelete = enumerableCache
			.Where(x => !string.IsNullOrEmpty(x.Key) && x.Key.Contains($"pageid={contentId};"))
			.Select(x => x.Key);

		// remove all caches for current page
		foreach (var key in keysToDelete)
		{
			OutputCache.Instance.Remove(key);
		}

		 var manager = new OutputCacheManager();

		 manager.RemoveItems("MasterSurface","Footer");

		 if(doctype == "NewsDetail")
		 {
			// clear cache of all news related actions
			manager.RemoveItems("NewsSurface");
		 }

	}
}

Web.config

<system.web>
	<caching>
		<outputCache enableOutputCache="true" />
		<outputCacheSettings>
			<outputCacheProfiles>
				<add name="LongGlobalCache" duration="86400" />
				<add name="LongPageCache" duration="86400" varyByCustom="url" />
				<add name="LongUserPageCache" duration="86400" varyByCustom="url;user" />
				<add name="NoCache" duration="0" />
			</outputCacheProfiles>
		</outputCacheSettings>
	</caching>
 </system.web>

varyByCustom="url;user" can cause cause problems when parsing cache keys as ; is the default delimiter for any other MVC routes that will also be stored in the key.

This will create a key that looks like this: url;user=pageid=1;url=/your-url;somethingelse=somethingelse; etc.