CachingChapter 12

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

Things that can be stored in Cache

• Web Forms

• Parts of web forms

• Application Data

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

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

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

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

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??)

HttpCachePolicy members vs OutputCache directive attributes

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" %>

Where are items stored?

• Default – anywhere they are accepted– Client– Proxy server– Host Server

Caching parts of a page

• Given: Large table that seldom varies

• Put table in user control and cache user control response

• Fragment caching

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

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

Cache Object

• Intrinsic object

• Stores frequently used items (quick retrieval)

• Global – available from anywhere in web app

• Similar to Application Object

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

Using Cache Object

Parameters for Add and Insert

Using Cache

• Demo 7 – UsingCache.aspx

• Walkthru

• Stores items in Cache – Load event

• Retrieve item from Cache – PreRender event

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

Cache Priority Settings

Using Cache Data before it is Removed from Memory

• Add/Insert Methods – onRemoveCallback

• Demo 8 – DataCache1.aspx

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

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

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

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

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

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

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