Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1089 Chapter 23: Caching Go ahead and enable both the Customers and Product tables. You run the command once per table. After a table is successfully enabled, you receive the following response: Enabling the table for SQL cache dependency. . Finished. After the table is enabled, you can begin using the SQL cache invalidation features. However, before you do, the following section shows you what happens to SQL Server when you enable these features. Looking at SQL Server 2000 Now that the Northwind database and the Customers and Products tables have all been enabled for SQL cache invalidation, look at what has happened in SQL Server. If you open up the SQL Server Enterprise Manager, you see a new table contained within the Northwind database — AspNet_SqlCacheTablesFor- ChangeNotification (whew, that’s a long one!). Your screen should look like Figure 23-4. Note that SQL Server 2000 isn’t supported on Vista, so this is a screenshot of a remote SQL 2000 machine viewed from the SQL Management Studio running on Vista. Figure 23-4 At the top of the list of tables in the right-hand pane, you see the AspNet_SqlCacheTablesForChange- Notification table. This is the table that ASP.NET uses to learn which tables are being monitored for 1089 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1090 Chapter 23: Caching change notification and also to make note of any changes to the tables being monitored. The table is actually quite simple when you look at the details, as illustrated in Figure 23-5. Figure 23-5 In this figure, you can see three columns in this new table. The first is the tableName column. This column simply shows a String reference to the names of the tables contained in the same database. Any table named here is enabled for SQL cache invalidation. The second column, notificationCreated , shows the date and time when the table was enabled for SQL cache invalidation. The final column, changeId , is used to communicate to ASP.NET any changes to the included tables. ASP.NET monitors this column for changes and, depending on the value, either uses what is stored in memory or makes a new database query. Looking at the Tables That Are Enabled Using the aspnet_regsql.exe tool, you can see (by using a simple command) which tables are enabled in a particular database. If you are working through the preceding examples, you see that so far you have enabled the Customers and Products tables of the Northwind database. To get a list of the tables that are enabled, use something similar to the following command: aspnet_regsql.exe -S localhost -U sa -P password -d Northwind -lt The -lt command produces a simple list of tables enabled for SQL cache invalidation. Inputting this command produces the following results: Listing all tables enabled for SQL cache dependency: Customers Products Disabling a Table for SQL Server Cache Invalidation Now that you know how to enable your SQL Server database f or SQL Server cache invalidation, take a look at how you remove the capability for a specific table to be monitored for this process. To remove a table from the SQL Server cache invalidation process, use the -dt command. In the preceding example, using the -lt command showed that you have both the Customers and Prod- ucts tables enabled. Next, you remove the Products table from the process using the following command: aspnet_regsql.exe -S localhost -U sa -P password -d Northwind -t Products –dt 1090 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1091 Chapter 23: Caching You can see t hat all you do is specify the name of the table using the -t command followed by a -dt command (disable table). The command line for disabling table caching will again list the tables that are enabled for SQL Server cache invalidation; this time, the Products table is not listed — instead, Cus- tomers, the only enabled table, is listed. Disabling a Database for SQL Server Cache Invalidation Not only can you pick and choose the tables that you want to remove from the process, but you can also disable the entire database for SQL Server cache invalidation. In order to disable an entire database, you use the -dd command (disable database). Note that disabling an entire database for SQL Server cache invalidation also means that every single table contained within this database is also disabled. This example shows the Northwind database being disabled on my computer: C: \> aspnet_regsql -S localhost -U sa -P wrox -d Northwind -dd Disabling the database for SQL cache dependency. Finished. To ensure that the table is no longer enabled for SQL Server cache invalidation, we attempted to list the tables that were enabled for cache invalidation using the -lt command. We received the following error: C: \ > aspnet_regsql -S localhost -U sa -P wrox -d Northwind -lt An error has happened. Details of the exception: The database is not enabled for SQL cache notification. To enable a database for SQL cache notification, please use SQLCacheDependencyAdmin.EnableNotifications method, or the command line tool aspnet_regsql.exe. If you now open the Northwind database in the SQL Se rver Enterprise Manager, you can see that the AspNet_SqlCacheTablesForChangeNotification table has been removed for the database. SQL Server 2005 Cache Invalidation As you’ve seen, standard SQL Server 2000 cache invalidation uses a table-level mechanism using a polling model every few seconds to monitor what tables have changed. SQL Server 2000’s technique not only requires preparation of the database, its polling is rather expensive and its caching is quite coarse. SQL Server 2005 supports a different, more granular series of notification that doesn’t require polling. Direct notification of changes is a built-in feature of SQL Server 2005 and is presented via the ADO.NET SqlCommand . For example: Protected Sub Page_Load(ByVal sender as Object, ByVal e as System.EventArgs) Response.Write("Page created: " + DateTime.Now.ToLongTimeString()) Dim connStr As String = ConfigurationManager.ConnectionStrings("AppConnectionString1").ConnectionString SqlDependency.Start(connStr) Dim connection As New SqlConnection(connStr) 1091 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1092 Chapter 23: Caching Dim command as New SqlCommand("Select * FROM Customers", connection) Dim depends as New SqlCacheDependency(command) Connection.Open GridView1.DataSource = command.ExecuteReader() GridView1.DataBind() Connection.Close "Now, do what you want with the sqlDependency object like: Response.AddCacheDependency(depends) End Sub SQL Server 2005 supports b oth programmatic and declarative techniques when caching. Use the string "CommandNotification" in the OutputCache directive to enable notification-based caching for a page as in this example. You can specify SQL caching o ptions either programmatically or declaratively, but not both. Note that you must first call System.Data.SqlClient.SqlDependency.Start , passing in the connection string, to start the SQL notification engine. < %@ OutputCache Duration="3600" VaryByParam="none" SqlDependency="CommandNotification"% > Or, if you’re using a SqlDataSource control from within your ASP.NET page: < asp:SqlDataSource EnableCaching="true" SqlCacheDependency="CommandNotification" CacheDuration="2600" / > As data changes within SQL Server 2005, SQL and ADO.NET automatically invalidate data cached on the Web server. Configuring Your ASP.NET Application After you enable a database for SQL Server cache invalidation and also enable a couple of tables within this database, the next step is to configure your application for SQL Server cache invalidation. To configure your application to work with SQL Server cache invalidation, the first step is to make some changes to the web.config file. In the web.config file, specify that you want to work with the Northwind database, and you want ASP.NET connected to it. Listing 23-5 shows an example of how you should change your web.config file to work with SQL Server cache invalidation. The pollTime attribute isn’t needed if you’re using SQL Server 2005 notification because it uses database events instead of the polling needed for earlier versions. Listing 23-5: Configuring the web.config file < configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0" > < connectionStrings > < add name="AppConnectionString1" connectionString="Data Source=localhost; 1092 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1093 Chapter 23: Caching User ID=sa;Password=wrox;Database=Northwind;Persist Security Info=False" providerName="System.Data.SqlClient" / > < /connectionStrings > < system.web > < caching > < sqlCacheDependency enabled="true" > < databases > < add name="Northwind" connectionStringName="AppConnectionString1" pollTime="500" / > < /databases > < /sqlCacheDependency > < /caching > < /system.web > < /configuration > From this listing, you can see that the first thing established is the connection string to the Northwind database using the < connectionStrings > element in the web.config file. Note the name of the connec- tion string because it is utilized later in the configuration settings for SQL Server cache invalidation. The SQL Server cache invalidation is configured using the new < caching > element. This element must be nested within the < system.web > elements. Because you are working with a SQL Server cache depen- dency, you must use a < sqlCacheDependency > child node. You enable the entire process by using the enabled = "true" attribute. After this attribute is enabled, you work with the < databases > section. You use the < add > element, nested within the < databases > nodes, to reference the Northwind database. The following table explains all the attributes of the < add > element. Attribute Description Name The name attribute provides an identifier to the SQL Server database. connectionStringName The connectionStringName attribute specifies the name of the connection. Because the connection string in the preceding example is called AppConnectionString1 , you use this value for the connectionStringName attribute as well. pollTime The pollTime attribute specifies the time interval from one SQL Server poll to the next. The default is .5 seconds or 500 milliseconds (as shown in the example). This is not needed for SQL Server 2005 notification. Now that the web.config file is set up correctly, you can start using SQL Server cache invalidation on your pages. ASP.NET makes a separate SQL Server request on a completely different thread to the AspNet_SqlCacheTablesForChangeNotification table to see if the changeId number has been incre- mented. If the number is changed, ASP.NET knows that an underlying change has been made to the SQL Server table and that a new result set should be retrieved. When it checks to see if it should make a SQL Server call, the request to the small AspNet_SqlCacheTablesForChangeNotification table has a single result. With SQL Server cache invalidation enabled, this is done so quickly that you really notice the difference. 1093 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1094 Chapter 23: Caching Testing SQL Ser ver Cache Invalidation Now that the web.config file is set up and ready to go, the next step is to actually apply these new capa- bilities to a page. Listing 23-6 is an example of a page using the SQL Server cache invalidation process. Listing 23-6: An ASP.NET page utilizing SQL Server cache invalidation VB < %@ Page Language="VB" % > < %@ OutputCache Duration="3600" VaryByParam="none" SqlDependency="Northwind:Customers"% > < script runat="server" > Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Label1.Text = "Page created at " & DateTime.Now.ToShortTimeString () End Sub < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Sql Cache Invalidation < /title > < /head > < body > < form id="form1" runat="server" > < asp:Label ID="Label1" Runat="server" >< /asp:Label >< br / > < br / > < asp:GridView ID="GridView1" Runat="server" DataSourceID="SqlDataSource1" > < /asp:GridView > < asp:SqlDataSource ID="SqlDataSource1" Runat="server" SelectCommand="Select * From Customers" ConnectionString=" < %$ ConnectionStrings:AppConnectionString1 % > " ProviderName=" < %$ ConnectionStrings:AppConnectionString1.providername % > " > < /asp:SqlDataSource > < /form > < /body > < /html > C# < %@ Page Language="C#" % > < %@ OutputCache Duration="3600" VaryByParam="none" SqlDependency="Northwind:Customers"% > < script runat="server" > protected void Page_Load(object sender, System.EventArgs e) { Label1.Text = "Page created at " + DateTime.Now.ToShortTimeString(); } < /script > The first and most important part of this page is the OuputCache page directive that is specified at the top of the file. Typically, the OutputCache directive specifies how long the page output is held in the cache using the Duration attribute. Next is the VaryByParam attribute. The new addition is the SqlDependency 1094 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1095 Chapter 23: Caching attribute. This enables a particular page to use SQL Server cache invalidation. The following line shows the format of the value for the SqlDependency attribute: SqlDependency="database:table" The value of Northwind:Customers specifies that you want the SQL Server cache invalidation enabled for the Customers table within the Northwind database. The Duration attribute of the OutputCache directive shows you that, typically, the output of this page is stored in the cache for a long time — but this cache is invalidated immediately if the Customers table has any underlying changes made to the data that it contains. A change to any of the cells in the Customers table of the Northwind database invalidates the cache, and a new cache is generated from the result, which now contains a new SQL Server database request. Figure 23-6 shows an example of the page generated the first time it is run. Figure 23-6 From this figure, you can see the contents of the customer with the CustomerID of ALFKI . For this entry, go to SQL Server and change the value of the ContactName from Maria Anders to Mary Anders .Ifwe weren’t using SQL Server cache invalidation, this change would have done nothing to the output cache. The original page output in the cache would still be present and the end user would still see the Maria Anders entry for the duration specified in the page’s OutputCache directive. But because we’re using SQL Server cache invalidation, after the underlying information in the table is changed, the output cache is invalidated, a new result set is retrieved, and the new result set is cached. When a change has been made, you see the results as shown in Figure 23-7. 1095 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1096 Chapter 23: Caching Figure 23-7 Notice also that the text ’’Page created at’’ includes an updated time indicating when this page was rendered. Need to stop working so late, eh? Adding More Than One Table to a Page The preceding example shows how to use SQL Server cache invalidation for a single table on the ASP.NET page. What do you do if your page is working with two or more tables? To add more than one table, you use the OutputCache directive shown here: SqlDependency="database:table;database:table" From this example, you can see that the value of the SqlDependency attribute separates the databases and tables with a semicolon. If you want to work with both the Customers table and the Products table of the Northwind database, you construct the value of the SqlDependency attribute as follows: SqlDependency="Northwind:Customers;Northwind:Products" Attaching SQL Server Cache Dependencies to the Request Object In addition to changing settings in the OutputCache directive to activate SQL Server cache invalidation, you can also set the SQL Server cache invalidation programmatically. To do so, use the SqlCacheDepen- dency class, which is illustrated in Listing 23-7. 1096 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1097 Chapter 23: Caching Listing 23-7: Working with SQL Server cache invalidation programmatically VB Dim myDependency As SqlCacheDependency = _ New SqlCacheDependency("Northwind", "Customers") Response.AddCacheDependency(myDependency) Response.Cache.SetValidUntilExpires(true) Response.Cache.SetExpires(DateTime.Now.AddMinutes(60)) Response.Cache.SetCacheability(HttpCacheability.Public) C# SqlCacheDependency myDependency = new SqlCacheDependency("Northwind", "Customers"); Response.AddCacheDependency(myDependency); Response.Cache.SetValidUntilExpires(true); Response.Cache.SetExpires(DateTime.Now.AddMinutes(60)); Response.Cache.SetCacheability(HttpCacheability.Public); You first create an instance of the SqlCacheDependency object, assigning it the value of the database and the table at the same time. The SqlCacheDependency class takes the following parameters: SqlCacheDependency(databaseEntryName As String, tablename As String) You use this parameter construction if you are working with SQL Server 7.0 or with SQL Server 2000. If you are working with SQL Server 2005, you use the following construction: SqlCacheDependency(sqlCmd As System.Data.SqlClient.SqlCommand) After the SqlCacheDependency class is in place, you add the dependency to the Cache object and set some of the properties of the Cache object as well. You can do this either programmatically or through the OutputCache directive. Attaching SQL Server Cache Dependencies to the Cache Object In addition to attaching SQL Server cache dependencies to the Request object, you can attach them to the Cache object for data that can be cached much longer. The Cache object is contained within the System.Web.Caching namespace, and it enables you to work programmatically with the caching of any type of objects. Listing 23-8 shows a page that utilizes the Cache object with the SqlDependency object. Listing 23-8: Using the Cache object with the SqlDependency object VB < %@ Page Language="VB" % > < %@ Import Namespace="System.Data"% > < %@ Import Namespace="System.Data.SqlClient"% > 1097 Evjen c23.tex V2 - 01/28/2008 3:38pm Page 1098 Chapter 23: Caching < script runat="server" > Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Dim myCustomers As DataSet myCustomers = CType(Cache("firmCustomers"), DataSet) If myCustomers Is Nothing Then Dim conn As SqlConnection = _ New SqlConnection( _ ConfigurationManager.ConnectionStrings("AppConnectionString1").ConnectionString) Dim da As SqlDataAdapter = _ New SqlDataAdapter("Select * From Customers", conn) myCustomers = New DataSet da.Fill(myCustomers) Dim myDependency As SqlCacheDependency = _ New SqlCacheDependency("Northwind", "Customers") Cache.Insert("firmCustomers", myCustomers, myDependency) Label1.Text = "Produced from database." Else Label1.Text = "Produced from Cache object." End If GridView1.DataSource = myCustomers GridView1.DataBind() End Sub < /script > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Sql Cache Invalidation < /title > < /head > < body > < form id="form1" runat="server" > < asp:Label ID="Label1" Runat="server" >< /asp:Label >< br / > < br / > < asp:GridView ID="GridView1" Runat="server" >< /asp:GridView > < /form > < /body > < /html > C# < %@ Page Language="C#" % > < %@ Import Namespace="System.Data" % > < %@ Import Namespace="System.Data.SqlClient" % > < script runat="server" > protected void Page_Load(object sender, System.EventArgs e) { DataSet myCustomers; myCustomers = (DataSet)Cache["firmCustomers"]; if (myCustomers == null) { SqlConnection conn = new 1098 . following command: aspnet_regsql.exe -S localhost -U sa -P password -d Northwind -lt The -lt command produces a simple list of tables enabled for SQL cache invalidation. Inputting this command. using the following command: aspnet_regsql.exe -S localhost -U sa -P password -d Northwind -t Products –dt 1090 Evjen c 23. tex V2 - 01/28/2008 3: 38pm Page 1091 Chapter 23: Caching You can see. This is the table that ASP. NET uses to learn which tables are being monitored for 1089 Evjen c 23. tex V2 - 01/28/2008 3: 38pm Page 1090 Chapter 23: Caching change notification and also to make note