Recipe 10.1 Uncovering Page-Level Problems

     

10.1.1 Problem

You want to find the source of a problem that appears to be associated with a particular page of your application, such as a page that completes its operations more slowly than desired.

10.1.2 Solution

Enable page-level tracing for the page in question by setting the Trace attribute of the @ Page directive in the .aspx file to " true " and then using Trace.Write (or Trace.Warn ) statements as warranted in your code-behind to write trace information to the trace output.

Example 10-1 through Example 10-3 show the code we've written to illustrate this solution. Example 10-1 shows the .aspx file for a typical ASP.NET page. The code-behind class for the page appears in Example 10-2 (VB) and Example 10-3 (C#). By running the page and analyzing the trace sequence, you can see how long certain key operations are taking. The output with the trace sequence is shown in Figure 10-1.

Figure 10-1. :Sample tracing output
figs/ancb_1001.gif

10.1.3 Discussion

Tracing tracks and presents the execution details about an HTTP request. The TraceContext class is actually where ASP.NET stores information about an HTTP request and its trace information. You access the TraceContext class through the Page.Trace property of an ASP.NET page. To enable tracing for the page, be sure to set the Trace attribute of the @ Page directive in the .aspx file to " true ", as shown in Example 10-1.

The TraceContext class has two methods for writing statements into the trace log: Write and Warn . The only difference is that Warn outputs statements in red so that they are easier to spot in the trace log. Both methods are overloaded and have three versions. If you pass a single string argument, ASP.NET writes it to the Message column of the trace log, as shown in Figure 10-1. If you use two string arguments, the first string appears in the Category column and the second in the Message column. If you use a third argument, it must be of type Exception and contain information about an error, which ASP.NET then writes to the trace log.

If you've placed Trace.Write or Trace.Warn statements in your code, you don't have to worry about removing them later. The common language runtime (CLR) will ignore them when tracing is disabled. Just be sure to disable page-level tracing before deploying your application to a production environment.

In our example, Trace.Write is used three times to put custom messages into the trace sequence: the first time to mark the start of the concatenations and the second to mark the end of the concatenations. The third message outputs the average time for a string concatenation. The latter shows how inefficient it is to use a classic concatenation operator ( & or + ) in ASP.NET string operations. (See Recipe 16.2 for more discussion of this code as well as the advantages of using the StringBuilder object to build strings over the classic concatenation operators.)

Notice in Figure 10-1 that the trace log (beginning with "Request Details") appears below the standard output for the ASP.NET page that is enabled for Trace . Here's an explanation of the "Trace Information" section contents in the trace log:


Category

A custom trace category that you specified as the first argument in a Trace.Write (or Trace.Warn ) method call.


Message

A custom trace message that you specified as the second argument in a Trace.Write (or Trace.Warn ) method call.


From First (s)

The time, in seconds, since the request processing was started (a running total).


From Last (s)

The time, in seconds, since the last message was displayed. This column is especially helpful for seeing how long individual operations are taking.

10.1.4 See Also

Recipe 16.2

Example 10-1. Page-level tracing (.aspx)
 <%@ Page  Trace="True"  Language="vb" AutoEventWireup="false"           Codebehind="CH10TestPageLevelTracingVB.aspx.vb"           Inherits="ASPNetCookbook.VBExamples.CH10TestPageLevelTracingVB"%> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html>   <head>     <title>Test Page Level Tracing</title>     <link rel="stylesheet" href="css/ASPNetCookbook.css">   </head>   <body leftmargin="0" marginheight="0" marginwidth="0" topmargin="0">     <form id="frmTracing" method="post" runat="server">       <table width="100%" cellpadding="0" cellspacing="0" border="0">         <tr>           <td align="center">             <img src="images/ASPNETCookbookHeading_blue.gif">           </td>         </tr>         <tr>           <td class="dividerLine">             <img src="images/spacer.gif" height="6" border="0"></td>         </tr>       </table>       <table width="90%" align="center" border="0">         <tr>           <td><img src="images/spacer.gif" height="10" border="0"></td>         </tr>         <tr>           <td align="center" class="PageHeading">             Page-Level Tracing (VB)           </td>         </tr>       </table>     </form>   </body> </html> 

Example 10-2. Code-behind for page-level tracing (.vb)
 Option Explicit On  Option Strict On '----------------------------------------------------------------------------- ' '   Module Name: CH10TestPageLevelTracingVB.aspx.vb ' '   Description: This class provides the code behind for '                CH10TestPageLevelTracingVB ' '***************************************************************************** Imports System Imports System.Text Namespace ASPNetCookbook.VBExamples   Public Class CH10TestPageLevelTracingVB     Inherits System.Web.UI.Page     '*************************************************************************     '     '   ROUTINE: Page_Load     '     '   DESCRIPTION: This routine provides the event handler for the page load     '                event.  It is responsible for initializing the controls      '                on the page.     '-------------------------------------------------------------------------     Private Sub Page_Load(ByVal sender As System.Object, _                           ByVal e As System.EventArgs) Handles MyBase.Load       Const STRING_SECTION As String = "1234567890"       Dim testStr As String       Dim counter As Integer       Dim startTime As DateTime       Dim elapsedTime As TimeSpan       Dim loops As Integer  'output trace message indicating the start of the concatenations   Trace.Write("Page_Load", "Before performing concatenations")  'Measure the elapsed time for 10,000 classic string concatenations       loops = 10000       startTime = DateTime.Now( )       testStr = ""       For counter = 1 To loops         testStr &= STRING_SECTION       Next  'output trace message indicating the end of the concatenations   Trace.Write("Page_Load", "After performing concatenations")  'calculate the elapsed time for the string concatenations       elapsedTime = DateTime.Now.Subtract(startTime)  'Write average time per concatenation in milliseconds to trace sequence   Trace.Write("Aver/concat", _   (elapsedTime.TotalMilliseconds / loops).ToString("0.0000"))  End Sub  'Page_Load   End Class  'CH10TestPageLevelTracingVB End Namespace 

Example 10-3. Code-behind for page-level tracing (.cs)
 //---------------------------------------------------------------------------- // //   Module Name: CH10TestPageLevelTracingCS.aspx.cs // //   Description: This class provides the code behind for //                CH10TestPageLevelTracingCS // //**************************************************************************** using System; using System.Text; namespace ASPNetCookbook.CSExamples {   public class CH10TestPageLevelTracingCS : System.Web.UI.Page   {     //************************************************************************     //     //   ROUTINE: Page_Load     //     //   DESCRIPTION: This routine provides the event handler for the page     //                load event.  It is responsible for initializing the     //                controls on the page.     //------------------------------------------------------------------------     private void Page_Load(object sender, System.EventArgs e)     {       const string STRING_SECTION = "1234567890";       string testStr = null;       DateTime startTime;       TimeSpan elapsedTime;       int counter;       int loops;  // output trace message indicating the start of the concatenations   Trace.Write("Page_Load", "Before performing concatenations");  // measure the elapsed time for 10000 classic string concatenations       loops = 10000;       startTime = DateTime.Now;       testStr = "";       for (counter = 1; counter <= loops; counter++)       {         testStr += STRING_SECTION;       }  // output trace message indicating the end of the concatenations   Trace.Write("Page_Load", "After performing concatenations");  // calculate the elapsed time for the string concatenations       elapsedTime = DateTime.Now.Subtract(startTime);  // Write average time per concatenation in milliseconds to trace sequence   Trace.Write("Aver/concat",   (elapsedTime.TotalMilliseconds / loops).ToString("0.0000"));  }  // Page_Load   }  // CH10TestPageLevelTracingCS } 



ASP. NET Cookbook
ASP.Net 2.0 Cookbook (Cookbooks (OReilly))
ISBN: 0596100647
EAN: 2147483647
Year: 2006
Pages: 179

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