Caching

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: • <%@ OutputCache Duration="5" VaryByParam="None" Location="Any" %>

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