1. Caching Chapter 12

2. Caching For high-performance apps Caching: storing frequently-used items in memory –Accessed more quickly Cached Web Form bypasses: –server’s processing HTML –Server’s running web form to create a response Response is processed directly from memory

3. Things that can be stored in Cache Web Forms Parts of web forms Application Data

4. Caching Web Forms Good Caching Candidates –Frequently used –Contains fairly static data First series of Demos  Use OutputCache directive Demos show different ways to control caching Demo 1 – WebFormCaching1.aspx –Response loaded into memory for 60 secs (on client) –Subsequent requests during period get stored response –After 60 secs new response is cached

5. Another way to control Caching Previous examples used OutputCache directive From code, use Response object’s Cache property Returns a HttpCachePolicy object HttpCachePolicy members are similar to attributes of OutputCache directive

6. Multiple Caches from Single Web Form Demo2 – WebFormCaching2.aspx –VaryByParam attribute –New form cached when query string or HTTP POST varies –Demo – up to 5 different cached responses One for each time zone

7. Vary by Response Header Demo 3 – VaryByHeader.aspx –Different forms cached depending on Language Requested in Response.Header –Change regional settings in Windows Control Panel –One form cached per language requested

8. Cache Response / Custom String Demo 4 – CustomString.aspx Custom string set in Global.aspx Demo caches a response based on the browser used to request the page –(Netscape == Mozilla??)

9. HttpCachePolicy members vs OutputCache directive attributes

10. Controlling Caching thru Code Demo 5 – UsingResponseCache Uses Response.Cache object Sets Cache duration at 5 seconds Similar to Duration attribute of OutputCache directive:

11. Where are items stored? Default – anywhere they are accepted –Client –Proxy server –Host Server

12. Caching parts of a page Given: Large table that seldom varies Put table in user control and cache user control response Fragment caching

13. Caching Part of a Web Form with a User Control Place controls and content in a web user control Set caching attributes for that control Create an instance of the user control on the web form Demo 6 –PartialCaching1.aspx –Uses PartialCaching1.ascx

14. Caching Application Data Cache frequently used data Usually Read-Only To store changed cache data before it is removed from memory: –Use CacheItemRemovedCallback delegate to save changes

15. Cache Object Intrinsic object Stores frequently used items (quick retrieval) Global – available from anywhere in web app Similar to Application Object

16. Ways to store data in Cache object Assignment –Assign a value to a key in the Cache object –Cache(“NewItem”) = “Some String Data” Insert method –Uses (optional) parameters to set policies and duration Add method –Parameters are required –Returns a reference to cached data

17. Using Cache Object

18. Parameters for Add and Insert

19. Using Cache Demo 7 – UsingCache.aspx Walkthru Stores items in Cache – Load event Retrieve item from Cache – PreRender event

20. How Long does an item stay in Cache? Add/Insert Parameters Really these give only indirect control When memory gets low, ASP.NET: –Removes expired members from cache –Unloads other members based on their priority and when last accessed

21. Cache Priority Settings

22. Using Cache Data before it is Removed from Memory Add/Insert Methods –onRemoveCallback Demo 8 – DataCache1.aspx

23. Updating Cache when Data Changes Data stored in cache may represent data stored elsewhere (say in a database). Establish relationship between cached data and external: –File –Folder –Group of files Use Add/Insert dependency parameter –Accepts a CacheDependency object

24. CacheDependency object Identifies file, folder, or set of files to watch for change ASP.NET checks timestamps of objects in CacheDependency object Compares with DateTime for cached item If later, unloads the item from the cache

25. Using CacheDependency object Demo 9 – DataCache2.aspx NewItem in Cache is linked to NewItem.TXT file When new data is written to the file, data is removed from Cache

26. Demo 10 – C# Demo10 – CachingLab.aspx –Displays a list of customers from Northwind db –Users select from dropdown list –Click button to view orders in data grid Web Form cached for 1 minute Since response can vary by which customer is selected, use VaryByParam to store multiple responses – one for each selected customer

27. Page_Load Event CustList is a ListItemCollection object If this is the first time through (IsPostback) –If the list is not in the cache Store it in the cache (CacheCustList()) –Else take the Customer List out of the cache –Move the CustList Details to the DropDownList

28. CacheCustList Method Connect to NorthWind Create a DataReader for the Customer records For each row provided by the datareader –Add the Customer Data to the CustList Put the CustList in the Cache – 5 min Close the connection

29. butGetOrders_Click Create a new dataset to hold the orders for the selected customer If the Order Data for this customer is not in the Cache, If IsNothing(Cache(drpCustList.SelectedItem.Value)) –Put it there – CacheOrders Else –Set the dataset = the Cached orders Bind the order data to the grid