Caching MacDonald Ch. 26

1. CachingMacDonald Ch. 26 MIS 424 Professor Sandvig

2. Overview • What is Caching • Where to cache • When to cache • Data caching in ASP.NET • Page caching • Page Fragment caching • Cache Class • Create you own cache

3. What is Caching • Cache = “secret store” • Armies: cache weapons • Squirrels: cache nuts • Computers: cache data • Benefits of caching data: • Reuse • Process once, reuse many times • Faster, cheaper

4. Where to Cache • Client-side • Browsers • Images • Pages • Reduces download times • Server-side • Reduces server processing load

5. When to Cache on server • Frequently hit pages • Content changes infrequently • NYTimes.com • ESPN.com • CMS (see Drupal Boost) • Data is expensive to retrieve • MIS 424 • Weather forecast • Amazon Best Sellers

6. When NOT to cache • Pages that change frequently • Shopping cart • Amazon.com • Customized for each user • Personal data • Infrequently accessed data • Cache must be stored  Overhead • cost depends upon caching method

7. Caching Tools in ASP.NET • Caching Options • Page • Page fragment • Data class • Create your own • Database • Application or session object

8. Page Caching • Caches entire page • Page directive: <%@ Page OutputCache Duration=“300” VaryByParm=“none” %> • Duration in seconds • Stored on disk • Low penalty

9. Page Caching - parameters • VaryByParm= • “None” • Single cache for all parameter combinations • “*” • Different cache for each parameter combination • “ParameterList” • Different cache for listed parameters • One cache for other parameters

10. Page Caching - parameters • Example: • 14_CachePage.aspx source, output • Location: • Server • Client • Downstream – proxy servers • Any • None

11. Page Caching - parameters • Also may specify cache for header attributes: • Language • Browser version • Etc.

12. ASP.NET Caching • Page • Page fragment • Data class • Create your own

13. Page Fragment Caching • Cache part of a page • Content in user control • Syntax similar to Page cache • Example: • Music Store menu

14. Page Fragment Caching • Benefits: • Useful for menus, headers, footers… • Easy to implement • Stored on disk • Weaknesses • OnClick events frozen • Timeout fixed duration only

15. ASP.NET Caching • Page • Page fragment • Cache class • Create your own

16. Cache Class • Cached data accessible throughout application • Use data on multiple page • Cache any type of data object • strings, datasets, dataviews, … • Set expiration date • Several options

17. Cache Class • Cache.Insert method • Parameters for: • Expiration date – absolute & sliding • File dependencies • Database tables • Subroutine to run when expires • Documentation

18. Cache Class - Syntax Cache.Add(Key, Object, CacheDependency, DateTime, TimeSpan, CacheItemPriority, CacheItemRemovedCallback) • Example: • CacheExample.aspx source, output

19. Create Your Own • Program own rules • Customize storage location • Database • File • Combination of Cache locations • Expiration rule • Fixed time of day, week, month… • Number of hits… • Example: Weather forecast

20. Summary • Several Caching options .NET • Page • Page fragment • Cache object • Roll your own • Dramatic performance improvements when data expensive to retrieve