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New Caching Features in ASP.NET 2.0

For most web applications, caching in some form can be a very effective strategy in improving performance and scalability. ASP.NET 1.0 offered several forms of caching that allowed web applications to minimize expensive processing, reduce network trips to the backend, and alleviate database load: generic data caching, output caching, and fragment caching. (To learn more about these features, please visit the ASP.NET 1.0 Quickstarts).

ASP.NET 2.0 has expanded on these features, making them more powerful, easier to use, and easier to manage. The following improvements are included:

Feature	Description
Data Cache
Custom Cache Dependencies	Ability to implement custom dependencies to enable efficient invalidation of cached objects based on changes to arbitrary resources.
SQL Server Cache Dependency	A dependency type to monitor changes of data in a SQL Server database. This dependency can be used programmatically, as well as declaratively for output cache and fragment cache.
Cache Configuration	Ability to control cache behavior from configuration.
Output Caching
Post-Cache Substitution	API to insert dynamic regions into response for every request that returns an output cached page.
Cache Profiles	Ability to define and manage groups of output cache settings in configuration, instead of placing them in an individual page.
Fragment Caching
Fragment Caching API	API to control caching settings for a user control programmatically.

Custom Cache Dependencies

ASP.NET 2.0 opened the System.Web.Caching.CacheDependency class for derivation, enabling anyone to write their own implementation of a cache dependency. By developing your own cache dependency, you can take advantage of the cache invalidation mechanism to keep the cached content current with the data that was used to construct it. This is a more efficient and reliable way to ensure data validity, and enable cache synchronization across web farms, than using frequent expiration.

ASP.NET provides two dependency types built on top of CacheDependency: AggregateCacheDependency, which allows multiple dependencies to be aggregated for complex content types that depend on more then one type of resource, and SqlCacheDependency, which is described below.

SQL Server Cache Dependency

The SqlCacheDependency implementation of a custom dependency enables users to invalidate cache content based on data changes in the SQL Server Database. Two types invalidation services provided:

Table-based, allowing to detect changes to data within one or more tables
Command-based, allowing to detect changes to result sets of arbitrary queries issued by one or more SqlCommand instances

The SQL Server Cache Dependency can be used programmatically with the Cache API. Many of ASP.NET features, including output cache, fragment cache, and data source controls also enable use of SQL cache dependency declaratively.

In the example below, an page that displays the contents of the Authors table in the Pubs database takes advantage of SQL cache dependency on the data source control to stay up to date with changes to the data. The page indicates the configured connection string and table to monitor for changes in the SqlCacheDependency proeprty of the data source control, using the syntax, Pubs:Authors.

The data source control caches the data indefinitely, avoiding the expense of database querying on every render. However, when you edit the data, either through the GridView edit functionality or externally, the cached response is invalidated and the data source control reloads the data.

Cache Configuration

ASP.NET 2.0 provides configuration settings to allow you to have more control over the cache behavior for the entire application. Armed with these settings, you can debug your application by turning specific cache features like expiration and dependencies on and off. You can also control the behavior of individual features such as SQL cache dependencies.

The caching settings are located in the section group.

Post Cache Substitution

In ASP.NET 1.0, pages that were mostly static but contained a small dynamic region, such as username or current time, were frequently forced to either not use caching or partition the page into multiple user controls cached with fragment caching. ASP.NET 2.0 enables these pages to take advantage of output caching, by allowing output cached pages to insert dynamic content on every request. In the example below, the output cached page inserts a dynamic callback to a static method that returns the current date with the Response.WriteSubstitution API. This callback executes on every request, and the result gets inserted into the cached response chain that is served from output cache.

Cache Profiles

Cache profiles allow cache settings for hundreds of pages to be deployed and managed centrally from configuration. Individual pages can still override the settings in the profile by specifying them in the <%@ OutputCache %> directive, but for manageability purposes they can simply inherit most or all settings from a cache profile. In the example below, the page uses a cache profile specified with a CacheProfile attribute, with the cache settings located in the profile entry in the section of the configuration section group.

Fragment Caching API

The Fragment Caching ControlCachePolicy API allows the user control or page developer to programmatically control caching settings for a fragment cached user control. A variety of advanced scenarios are made possible by this feature, which were not available in ASP.NET 1.0 that only allowed declarative specification of the cache settings for fragment cache. In the example below, the user control can determine whether or not it should be cached based on a querystring parameter. The control varies by the “cache” parameter, and programmatically disables its own caching via the ControlCachePolicy.Enabled property when the parameter has the value of “false”.