1. ASP.NET Caching

2. Overview Caching Pages with the @OutputCache Directive
Introduction to caching data with the Cache object

3. Why Cache? Simply put, we cache to But caching can
Prevent redundant page creation
Minimize database requests
But caching can
Increase memory usage
A poorly designed caching system can lead to various types of attacks (denial-of-service)

4. Caching an Output Page (1)
You add directive to a page with a few attributes
Duration indicates the number of seconds to cache the page
varyByParam
If set to none, cached output will not vary based on parameters
Use multiple semicolon separated parameters to create cached pages for various parameter configurations
Use * to vary cached pages for all parameter configurations

5. Caching an Output Page (2)
The caching mechanism is quite sophisticated
You can create cache dependencies to SQL tables
The cached page can be stored in the server or on the client
The HttpCachePolicy class is used to create custom cache rules

6. Caching an Output Page (Example)
Cached page lasts for 60 seconds
Vary the pages based on the value of the query parameter named employeeID
Duration=“60” VaryByParam=“employeeID” %>

7. Cache an Output Page (Advanced Features)
It’s possible to cache parts of a page (page fragment)
Refresh an AdRotater on each postback but cache the other parts of the page

8. Introduction to the Cache Object (1)
It’s really a ‘replacement’ for the ASP.NET Application object
It’s thread safe
You to not need to explicitly lock critical code sections
It’s configurable
Cache objects can be configured to expire when you want them to
Cache objects can be prioritized

9. Introduction to the Cache Object (2)
Like the Application object, Cache objects don’t work outside the application domain
Like the Application and Session objects, it’s maintained as a collection of key/value pairs
We are caching specific data here rather than the entire page

10. Introduction to the Cache Object (3)
The Cache object (sort of) works in a Web garden
Each processor gets its own object
Cache objects will likely vary from one processor to the next
All the work is handled by ASP

11. Important Cache Members
The NoAbsoluteExpiration field is used to force a cached item never to expire
The NoSlidingExpiration field disables sliding expiration

12. Cache Dependencies
When creating a cached item, that item might have a cache dependency
The CacheDependancy object can represent a file, and array of files, or a directory