Caching Asp.net

If you're using typically static data with your ASP.NET applications - such as that from a database server like Microsoft SQL Server - you should take a look at caching your data. Previously, this was not an easy thing to do, but the caching in .NET makes caching your data and objects a trivial task. This tutorial will cover basic caching and scenarios where caching would be good to use. Using the Cache Property In ASP.NET, every page you write extends the System.Web.UI.Page class, which contains a member called Cache. You use the Cache property as you would any other IEnumerable, which gives you methods and properties to get, set, and enumerate through members. We will be looking at getting and setting items in the cache. In the simplest example, you can retrieve any object from the cache like so: Object obj = (Object)Cache["key"];

What this does is look in the Cache for an item with the key "key". If such an item exists, the object is returned. While we don't need to cast the returned object to Object, this is just an example of how you must cast the return to the class type you want returned. If the item is not found, null is returned, so you will need to do some checking: Object obj = (Object)Cache["key"]; if (obj == null) { // Generate a new object and insert it into the cache } // Use your object

You can also assign object to the cache like the following code example, but using Cache.Inset() is a much better means as you'll see later: Cache["key"] = obj;

Now let's look at a serious example. In the example below, we will define a function that binds data to a control, such as a ASP.NET DataGrid control. We will look at data binding in a little more depth later. For this example, we will use a System.Data.DataSet object. <%@ Page Language="C#" %> <%@ Import Namespace="System.Data" %> <script runat="server"> private string _filename = "mydata.xml"; private void Page_Load(Object src, EventArgs args) { DataSet ds = (DataSet)Cache["mydata"]; if (ds == null) { ds.ReadXml(Server.MapPath(_filename)); Cache.Insert("mydata", ds, new CacheDependency(Server.MapPath(_filename)), DateTime.Now.AddHours(12), NoSlidingExpiration); }

myDataGrid.DataSource = ds; myDataGrid.DataBind(); }

We'll break down the above example. The first part we've already discussed, where we get the object from the cache. If the object is null (i.e., doesn't exist in the cache), we need to create the object. The first line after checking if our DataSet object is null loads an XML file called a DiffGram, which is a serialized DataSet object. We'll talk about this later. Essentially, the DataSet object (hereforth, "ds") is created from serialized XML, which you can event type by hand. We call Server.MapPath() because the file as we know it is virtual. ds.ReadXml needs the absolute path and filename to load it. Server.MapPath() figures out what the absolute path of a virtual filename (such as your web pages) and returns the absolute path. The next statement inserts the newly created "ds" into the cache. Again, the statement is: Cache.Insert("mydata", ds, new CacheDependency(Server.MapPath(_filename)), DateTime.Now.AddHours(12), NoSlidingExpiration);

1. The first parameter is the key used to identify our cache item. 2. The second parameter is the object we want to cache. In this example, we are caching the DataSet object "ds". This can be any object, however, including strings, numbers, controls, etc. 3. The third parameter creates a dependency on an object. If this object changes, the cached object is marked as expired and your application will regenerate next time, returning null as your object reference. In fact, the object is expired. You can also pass null in this parameter to signify that you don't want any dependencies. 4. The fourth parameter is the absolute expiration period your object is valid. Here, we use DateTime.Now (which uses "now's" time) and add 12 hours to it. This means the object will automatically expire in 12 hours. You could also use NoAbsoluteExpiration which means the object will never expire until the dependent object changes. We use an absolute expiration here to make sure we have somewhat recent data in case the CacheDependency doesn't expire the data for some reason. (As if Microsoft software doesn't have bugs!) 5. The fifth and final parameter is a sliding expiration. This means that if the object is access, the absolute expiration time is essentially pushed back to however many minutes, hours, etc. you specify here. This is an object of type TimeSpan. Here, we want our object expired after 12 hours even if the object is accessed before then. After all this, we can finally bind our object to a data-driven control, such as the ASP.NET DataGrid control. While the full use of the control is out of the scope of this tutorial, I will cover the usage in brief detail.

The DataGrid control is a data-driven control meaning that on the server, the control will use data and will then render the HTML onto the page for the client to see in their browser. We will define a basic DataGrid control customizing only a few parameters:

Please note: this example assumes you already have your other HTML tags setup and that the DataGrid is the only control in the BODY, which it doesn't have to be. Above, we define a Web server control of type DataGrid, which is a data-driven control that renders a table on the page. By setting AutoGenerateColumns to true (which is default anyway), we specify that the DataGrid control will automatically generate headers and columns based on your data in the order of the columns in your DataSet. We also setup default paging and a few items styles, while making the Header column text bold. In the example Page_Load() event handler, we did a little data binding like so: myDataGrid.DataSource = ds; myDataGrid.DataBind();

These two lines associate the DataSource property of the DataGrid with our DataSet object "ds" and then binds the data with DataBind(). If you do not call DataBind(), you will find that nothing is rendered on your page. The DataSource property can point at other types of object, like ArrayList(), DataView() and many others. Consult your .NET SDK Documentation for more details. Scenarios Why would you use this tutorial to build your next data-driven ASP.NET page? There are several examples, but I will discuss one here. Lets say that you've developed a page or site that generates a table of contents on ever page. You also have a SQL Server storing this data because the table of contents changes from time to time. Instead of making calls across the network to the SQL Server (even cached data on SQL Server requires a few calls back and forth), you could use the caching example above. There are two ways primary ways of handling this:

1. Setup a scheduled task on the SQL Server 2000 to output your table as XML to a specified location on your web server. Because SQL Server 2000 can serialize your data to DiffGrams used in DataSet construction, this is an easy way to deliver updates to your DiffGram file described above in our caching example. You could even setup a trigger on your SQL Server to generate a new DiffGram when the contents of your table change, but that is beyond the scope of this tutorial. 2. Another way is to adapt the example above to create not only a DataSet, but to use classes from System.Data.OleDb or System.Data.SqlClient to get your data from time to time from the server. In this particular case (which we'll do below), creating a cache dependency wouldn't make much since because the SQL Server is no longer updating your DiffGram file, identified by the private member _filename in the example above. You could adapt second method above to something like the following: <%@ Page Language="C#" %> <%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.SqlClient" %> <script runat="server"> // If used frequently, store these strings in your Web.config // and use ConfigurationSettings.AppSettings["key"] to get them out. // If you do this, make sure these are constant strings! private const string connstr = "Data Source=sqlserver1;Initial Catalog=Web"; private const string cmdstr = "SELECT Title,URL FROM TOC"; private void Page_Load(Object src, EventArgs args) { DataSet ds = (DataSet)Cache["mydata"]; if (ds == null) { // Connect to the SQL Server and get our data using a DataAdapter SqlConnection conn = new SQlConnection(connstr); SqlCommand cmd = new SqlCommand(cmdstr, conn); SqlDataAdapter adapter = new SqlDataAdapter(cmd); // Create a new DataTable and fill it DataTable dt = new DataTable("Item"); adapter.Fill(dt); // Now add our DataTable to a DataSet instance and add to cache ds = new DataSet("TOC"); ds.Tables.Add(dt); Cache.Insert("mydata", ds, null, DataTime.Now.AddHours(1), NoSlidingExpiration); } // Bind our data myRepeater.DataSource = ds; myRepeater.DataBind(); }

Yes, I've chanced our ASP.NET control to a Repeater because a DataGrid wouldn't make a lot of sense. I will describe what you could use in this example for a Repeater control in a minute. Describing the example above, it is really nothing more than what we had before execpt that we have no CacheDependency because we have no files to watch, and we create our DataSet from a DataTable that is filled by a SqlDataAdapter (or OleDbDataAdapter if you prefer). DataSets are good to store in the Cache since they are easy to use, can be used in any data-driven control, and can be serialized at will with one call to ReadXml() or WriteXml(). Note: another thing to mention to those that have used System.Data.OleDb classes but not System.Data.SqlClient classes, you will notice I didn't specify a Provider in the connection string. This is because the SqlClient classes are only interested in SQL Server connections and, hence, already know what the Provider is. Finally, our Repeater control would look something like the following:

"><%# DataBinder.Eval(Container, "Item.Title") %>

The expressions above evaluate your Container (your DataSet object) and find the "Item.Title" and "Item.URL". "Item" is the name of the data item, which is the the name of the table usually. You may remember that we called our DataTable "Item" above: DataTable dt = new DataTable("Item");

"Title" and "URL" our the names of our fields in the table. See, even your data is appropriately named! Conclusions That pretty much wraps up the tutorial of how to use caching. There are many other examples and scenarios of how to use Caching and DataSets to cache data, but this tutorial is long enough I think. Please keep in mind that you can cache other objects as well, not just DataSets. I find that caching DataSets where you used infrequently accessed data is especially helpful, however, to decrease loads on your Web server, SQL Server (or other database server), and network.

I hope you've found this tutorial helpful and that the wheels in your head are spinning like mad with new ways to use caching to improve your web site's performance! ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||

Introduction ASP.NET has built-in cache engine that is used by ASP.NET pages to store and retrieve objects across HTTP requests. The ASP.NET cache is private to each application and stores objects in memory. The lifetime of the cache is equivalent to the lifetime of the application; that is, when the application is restarted, the cache is recreated. Placing an item in the cache is done in following way: Cache ("key") = Value

Retrieving the data is just as simple Value = Cache("key") If Value <> Null Then DisplayData(Value) End If

For sophisticated functionality in Applications on ASP.NET cache supports scavenging, expiration, and file and key dependencies. •

Scavenging means that the cache attempts to remove infrequently used or unimportant items if memory becomes scarce.

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Expiration allows programmers to give cache items lifetimes, which can be explicit (for example, expire at 12:00) or can be relative to an item's last use (for example, expire 10 minutes after the item was last accessed). After an item has expired, it is removed from the cache and future attempts to retrieve it return the null value unless the item is reinserted into the cache.

•

File and key dependencies allow the validity of a cache item to be based on an external file or on another cache item. If a dependency changes, the cache item is invalidated and removed from the cache. For an example of how you might use this functionality, consider the following scenario: an application reads financial information from an XML file that is periodically updated. The application processes the data in the file and creates a graph of objects that represent that data in a consumable format. The application caches that data and inserts a dependency on the file from which the data was read. When the file is updated, the data is removed from the cache and the application can reread it and reinsert the updated copy of the data.

Data Caching example

Collapse <%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.SqlClient" %> <script language="VB" runat="server"> Sub Page_Load(Src As Object, E As EventArgs) Dim dataSource As DataView ' Retrieve item from cache if anything is not there then we

have to

' add to the cache dataSource = Cache("CheDataSet") If dataSource Is Nothing Dim Conn As SqlConnection Dim Cmd As SqlDataAdapter Conn = New SqlConnection(_ "server=database;uid=sa;pwd=;database=Northw ind")

Cmd = New SqlDataAdapter("select * from customers", Conn) Dim ds As New DataSet Cmd.Fill(ds, "dsUsers") dataSource = New DataView(ds.Tables("dsUsers")) Cache("CheDataSet") = dataSource

CacheMsg.Text = "Dataset was Created directly from the Datebase. " &_ "Here the Cache was not used but the Cache was " &_ "Created, so check for the performance next time." Else cacheMsg.Text = "Dataset was Retrieved from cache which was " &_

"created earlier." End If MyDataGrid.DataSource=dataSource MyDataGrid.DataBind() End Sub

Caching Data Example

Examples 1. When Executed for the first time

2. When Executed after the cache is created.

Conclusion 1. Data Caching should be used very carefully only when required. 2. Data caching allows objects to be cached programmatically. 3. The cache is scoped to an application and its lifetime is equivalent to the lifetime of the application.

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In this article, you will learn about concepts, advantages, types of caching and about implementation of caching in ASP.NET applications. The code also serves as an example of using inline coding, creating user controls, trace mechanism, etc.

What is Caching? Caching is a technique of persisting the data in memory for immediate access to requesting program calls. Many in the developer community consider caching as one of the features available to improve performance of Web applications.

Why Caching? Consider a page that has list of Employee name, contact numbers and mail-Ids of existing employees of a company on an intranet accessible by all employees. This is

very useful information that is available throughout the company and could also be one of the most accessed pages. The functionality of adding, updating or deleting is usually less intensive compared to more transaction-based systems like Purchase ordering, Voucher creation etc. Now in a normal scenario the process of querying database for each request is not cost-effective in terms of server resources, hence is lot better to cache or persist the data to avoid this costly loss of resources.

The .NET Advantage ASP.NET provides the flexibility in terms of caching at different levels. 1. Page Level Output Caching This is at the page level and one of the easiest means for caching pages. This requires one to specify Duration of cache and Attribute of caching. Syntax: <%@ OutputCache Duration="60" VaryByParam="none" %> The above syntax specifies that the page be cached for duration of 60 seconds and the value "none" for VaryByParam* attribute makes sure that there is a single cached page available for this duration specified. * VaryByParam can take various "key" parameter names in query string. Also there are other attributes like VaryByHeader, VaryByCustom etc. Please refer to MSDN for more on this. 2. Fragment Caching Even though this definition refers to caching portion/s of page, it is actually caching a user control that can be used in a base web form page. In theory, if you have used include files in the traditional ASP model then this caching model is like caching these include files separately. In ASP.NET more often this is done through User Controls. Initially even though one feels a bit misleading, this is a significant technique that can be used especially when implementing "n" instances of the controls in various *.aspx pages. We can use the same syntax that we declared for the page level caching as shown above, but the power of fragment caching comes from the attribute "VaryByControl". Using this attribute one can cache a user control based on the properties exposed. Syntax: <%@ OutputCache Duration="60" VaryByControl="DepartmentId" %> The above syntax when declared within an *.ascx file ensures that the control is cached for 60 seconds and the number of representations of cached control is dependant on the property "DepartmentId" declared in the control. Add the following into an *.ascx file. Please note the use of tag "Control" and the cache declaration. <%@ Control Language="C#"%> <%@ outputcache duration="60" varybycontrol="DepartMentId" %> <script runat="server"> private int _Departmentid=0; public int DepartMentId

{ get{return _Departmentid;} set{_Departmentid =value;} } //Load event of control void Page_Load(Object sender, EventArgs e) { lblText.Text = "Time is " + DateTime.Now.ToString() + " for Department id = " + _Departmentid + "\n"; } Add the following to an *.aspx file. Please note the way "Register" tag is used; the declaration of control using syntax <[TagPrefix]:[TagName]>; Usage of property " DepartMentId". Open the page in two browsers and closely watch the Base form timing and the User control timing. Also note that the following page results in two copies or representation of user control in the cache. <%@ Page Language="C#" Trace="true" %> <%@ Register TagPrefix="CacheSample" TagName="Text" Src="CachingControl.ascx" %> <script runat=server> void Page_Load(Object sender, EventArgs e) { this.lbltime.Text ="Base form time is " + DateTime.Now.ToString() + "\n"; }

3. Application Level Caching With Page level Output caching one cannot cache objects between pages within an application. Fragment caching is great in that sense but has limitations by using user controls as means to do. We can use the Cache object programmatically to take advantage of caching objects and share the same between pages. Further the availability of different overloaded methods gives a greater flexibility for our Cache policy like Timespan, Absolute expiration etc. But one of the biggest takes is the CacheDependancy. This means that one can create a cache and associate with it a dependency that is either another cache key or a file. In almost all Web applications there could be numerous master tables that act as lookups to application specific tables. For e.g. if you take up adding a Employee, usually one has master tables like "tblQualification" to get list of qualifications, "tblLocations" to get list of locations etc. These tables* are usually set during the initial application configuration phase and could be modified once a month or even less than that. Hence it makes sense for us to use them in our Cache rather than making calls to database on each request. But then what Cache Policy do we adopt? We cannot hold these objects in Cache for entire application instance, because if anybody changes data in these tables one has to also refresh the cache. It is here that CacheDependancy can be used. * Even though these tables are less frequently used for updates, they are extensively used in our select statements through out the applications. Find below the snippet that uses CacheDependancy. Here what I have done is to provide a list view of existing employees. You need to create a Database in Sql Server, setup some data before you can continue. The schema scripts are enclosed in the article. Add database connection value in Web.Config and change the value as per your setup. First I get the dataset into which I fill the user list. But before this I check for the cache initially if it exists I directly cast it to a dataset, if not create a cache again. daUsers.Fill(dsUsers,"tblUsers"); I create the cache with "Users" as key using Cache.Insert* and link this with a file "Master.xml". This "Master.xml" is a XML file that contains Master data of "tblQualifications" and "tbllocations". I have used "Server.MapPath" to get the physical path of the file on the server. The CacheDependancy instance will make sure that any change in this dependency file means that you need to recreate your cache

key definition. This is a great feature to use since I can recreate my cache only when required instead of caching the data at the page level. Cache.Insert("Users",dsUsers,new System.Web.Caching.CacheDependency(Server.MapPath("Master.xml")) , DateTime.Now.AddSeconds(45),TimeSpan.Zero); * For other overloaded parameters refer MSDN. Also note how we could use trace within to add my own statements. HttpContext.Current.Trace.Write("from Database.."); <%@ Page Language="c#" Trace="true" %> <%@ import Namespace="System" %> <%@ import Namespace="System.Data" %> <%@ import Namespace="System.Data.SqlClient" %> <%@ import Namespace="System.Configuration" %> <%@ import Namespace="System.Web" %> <%@ import Namespace="System.Collections" %> <%@ import Namespace="System.IO" %> <script runat="server"> void Page_Load(Object sender, EventArgs e) { DataSet dsUsers; try { if(Cache["Users"]==null) { SqlConnection cn; dsUsers = new DataSet("new"); cn = new SqlConnection(ConfigurationSettings.AppSettings.Get("conn")); SqlDataAdapter daUsers; daUsers = new SqlDataAdapter("Select * from tblUsers",cn); cn.Open(); daUsers.Fill(dsUsers,"tblUsers"); //Update the cache object Cache.Insert("Users",dsUsers, new System.Web.Caching.CacheDependency( Server.MapPath("Master.xml")), DateTime.Now.AddSeconds(45),TimeSpan.Zero); HttpContext.Current.Trace.Write(DateTime.Now.AddSeconds(45).ToString() + " is expiry time.."); cn.Close(); cn.Dispose(); HttpContext.Current.Trace.Write("from Database.."); lblChange.Text ="From the database...."; } else { HttpContext.Current.Trace.Write("From cache.."); lblChange.Text ="From the cache...."; dsUsers= (DataSet) Cache["Users"]; } dlUsers.DataSource =dsUsers;

dlUsers.DataMember = dsUsers.Tables[0].TableName ; //lblChange.Text += Server.MapPath("Master.xml"); this.DataBind(); } catch(Exception ex) { lblChange.Text = ex.Message; } } <meta content="Microsoft Visual Studio 7.0" name="GENERATOR" /> <meta content="C#" name="CODE_LANGUAGE" /> <meta content="JavaScript" name="vs_defaultClientScript" /> <meta content="http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema" />

<SelectedItemStyle font-bold="True" forecolor="White" backcolor="#CC3333">

<%#DataBinder.Eval(Container.DataItem,"UserId")%>

<%#DataBinder.Eval(Container.DataItem,"FirstName")%>

<%#DataBinder.Eval(Container.DataItem,"LastName")%>

We created the page that initiates and uses the Cache. For testing purpose we need another page that will overwrite this "Master.xml" on click of a button for which the code snippet is as follows. This ideally should be our master maintenance page that adds/updates Master records in database and overwrites the XML. But to make it easy I have just written an overwriting sample. <%@ Page Language="C#" Trace="true"%> <%@ import Namespace="System" %> <%@ import Namespace="System.Data" %> <%@ import Namespace="System.Data.SqlClient" %> <script runat="server"> void btnMaster_Click(Object sender, EventArgs e) { //Call save function this.Save(); } void Save() { try { SqlConnection cn; DataSet dsUsers = new DataSet("Users"); //I have used this to get the Connectionstring from the //Configuration file. cn = new SqlConnection(ConfigurationSettings.AppSettings.Get("conn")); SqlDataAdapter daQualification; SqlDataAdapter daLocations; daQualification = new SqlDataAdapter("Select * from tblqualifications",cn); daLocations = new SqlDataAdapter("Select * from tblLocations",cn); cn.Open(); daQualification.Fill(dsUsers,"tblqualifications"); daLocations.Fill(dsUsers,"tblLocations"); HttpContext.Current.Trace.Write("Masters data up.."); //Overwrite the XML file. Also please read MSDN on the overloaded parameters for WriteXml dsUsers.WriteXml(HttpContext.Current.Server.MapPath "Master.xml"),XmlWriteMode.WriteSchema); cn.Close(); cn.Dispose(); } catch(Exception ex) { throw new Exception(ex.Message); } }

<span>

Rewrite the XML File by clicking the buttonbelow.

Now once you have created the above pages i.e. one that implements caching and other that overwrites the dependency file, create two instance of browser and open the cache implementation page and note for trace, label text; open the other instance of browser with the page which overwrites the XML. Note the former, the first time it fetches data from the database and the subsequent request will be from cache till your expiration time of 45 seconds is reached or anyone overwrites or changes the "Master.xml" file. Also give a look on Timespan parameter since you have a concept of Sliding expiration that can also be implemented. Keep refreshing the first page and you will see that trace indicates the cached page retrieval. Click the overwrite XML button on the latter page that would overwrite the XML and again refresh the former page to note that the data is retrieved from database. Though in this example I have not shown any direct relation between the cached data and the dependency file (like get values from dependency file and merge with cached object etc) in terms of integrated usage, this could very easily be designed and implemented. Dependency caching is a powerful technique that .NET supports and should be utilized wherever applicable.

Conclusion Caching is a technique that definitely improves the performance of web applications if one is careful to have a balance in terms of which data needs to be cached and parameter values for expiration policy.