Monday, April 29, 2013

SQL Parameter sniffing

SQL Parameter sniffing

For last few days we were having a problem with a few stored procedures that stop functioning for some set of values using SQL Server 2012. The stored procedure work correctly with one set of parameters, while with another set would timeout and fail.

The initial way that we bypassed this problem was that when this circumstance was found, we would alter the stored procedure and this seemed to fix it. As you can imagine it wasn't an ideal situation for an enterprise application because the problem would need to be found and reported before we would even know it existed but we struggled to find any proposed solutions to the problem.
After much investigation it was suggested that this could be caused by parameter sniffing. SQL Server does this by tracking what happens to the parameters passed into the stored procedure when creating the stored procedure and working out the execution plan. So the execution plan generated by SQL server was good most of the time but the plan would contain situations where the procedure would fail.
Below is a stored procedure that allows parameter sniffing. This is not one of the stored procedures that did have the problem, but a stored procedure where parameter sniffing occurs:
ALTER PROCEDURE [dbo].[ReportJobSeekerDetails]
@MarketPlaceID BIGINT,
@RoleName NVARCHAR(20),
@UserStatus TINYINT = NULL,
@RegStartDate DATETIME = NULL,
@StartRowNumber INT,
@PageSize INT,
@SortExpression NVARCHAR(100)
-- SET NOCOUNT ON added to prevent extra result sets from
IF @PageSize > 100
SET @PageSize = 100
SELECT COUNT(*) 'RowCount'
aspnet_users au
INNER JOIN aspnet_membership am ON au.userID = am.userid
INNER JOIN aspnet_usersinroles ur ON ur.userID = au.UserId
INNER JOIN UserPublicProfile upp ON upp.UserID = ur.ID
LEFT JOIN Country c ON upp.CountryID = c.Id
LEFT JOIN State s ON upp.StateID = s.ID
WHERE (@CountryId IS NULL OR c.Id = @CountryId)
AND (@StateId IS NULL OR upp.StateId = @StateId)
AND (@UserStatus IS NULL OR am.IsLockedOut = @UserStatus)
AND (@RegStartDate IS NULL OR am.CreateDate > @RegStartDate)
AND (@RegEndDate IS NULL OR am.CreateDate < @RegEndDate)
With the following addition of variables it prevents SQL Server from having the ability to perform parameter sniffing:
ALTER PROCEDURE [dbo].[ReportJobSeekerDetails]
@MarketPlaceID BIGINT,
@RoleName NVARCHAR(20),
@UserStatus TINYINT = NULL,
@RegStartDate DATETIME = NULL,
@StartRowNumber INT,
@PageSize INT,
@SortExpression NVARCHAR(100)= NULL,
@TotalCount INT OUTPUT
DECLARE @CountryIdLocal SMALLINT = @CountryId
DECLARE @StateIdLocal BIGINT = @StateId
DECLARE @UserStatusLocal TINYINT = @UserStatus
DECLARE @RegStartDateLocal DATETIME = @RegStartDate
DECLARE @RegEndDateLocal DATETIME = @RegEndDate
SELECT @TotalCount = COUNT(au.UserName)
FROM dbo.aspnet_users au
INNER JOIN dbo.aspnet_membership am ON au.userID = am.userid
INNER JOIN dbo.aspnet_usersinroles ur ON ur.userID = au.UserId
INNER JOIN UserPublicProfile upp ON upp.UserID = ur.ID
LEFT JOIN Country c ON upp.CountryID = c.Id
LEFT JOIN State s ON upp.StateID = s.ID
WHERE (@CountryIdLocal IS NULL OR c.Id = @CountryIdLocal)
AND (@StateIdLocal IS NULL OR upp.StateId = @StateIdLocal)
AND (@UserStatusLocal IS NULL OR am.IsLockedOut = @UserStatusLocal)
AND (@RegStartDateLocal IS NULL OR am.CreateDate > @RegStartDateLocal)
AND (@RegEndDateLocal IS NULL OR am.CreateDate < @RegEndDateLocal)
By implementing the small change demonstrated above on a couple of troublesome stored procedures, this fixed our problem with our stored procedures randomly not working with certain parameters. This proved that the problem was caused by parameter sniffing and left me wondering how many other people are out there with the same problem.

Happy Coding!!

difference between Response.Redirect(url) and Response.Redirect(url, false)

Avoid using Response.Redirect(url), instead, use Response.Redirect(url, false):

I have faced the issue, In our project generalize redirect code was written and it is called from other places. We just pass the redirect url to that generalize function. At few places there was a code after redirect function call. we don't wanted that code to be executed if redirect is happened and this call to redirect is based on particular condition. I started to check why it is happening then i came to know about the actual working of response.redirect()


        After writing a 302 redirect response to the response buffers, calls Response.End. This is very expensive. 

Response.Redirect(url, false): 

   It is fast, but unlike Response.Redirect(url), the lines of code which follow the call to Response.Redirect(url, false) will be executed.

Horrors of Response.End:
     what if you don't want the lines of code to execute after you redirect? Well, one way to accomplish this is to call HttpApplication.CompleteRequest(), which is accessible from the HttpContext. e.g., call calling Context.ApplicationInstance.CompleteRequest(). It's not the same as aborting the thread, which truly does prevent all subsequent lines of code form running. The lines of code that follow the call to CompleteRequest() will execute, but as soon as the current page or module that calls this completes, the pipeline will jump ahead to the EndRequest event.

Response.Redirect(url, false);
void Application_Error(object sender, EventArgs e)
Response.Redirect(url, false);

I hope this helps to understand why to use Response.Redirect(url, false) over Response.Redirect(url).

Happy Coding!!

Prevent the browser from caching the ASPX page

​use this code to prevent the browser from caching the ASPX page.

By default browser cache the page. sometimes we don't require the page to be cached.

It will work for IE, Mozilla, and Chrome. I didn't checked the below code for other browsers.

<%@ Page language="c#" AutoEventWireup="true" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="" >
    <title>HttpCachePolicy - SetNoStore - C# Example</title>
    <script runat="server">
      void Page_Load(Object sender, EventArgs e) 
        // Prevent the browser from caching the ASPX page

        // Display the DateTime value.
        Label1.Text = DateTime.Now.ToLongTimeString();
    <form id="Form1" method="post" runat="server">
      <h3>HttpCachePolicy - SetNoStore - C# Example</h3>

      <p>Click the Submit button a few times, and then click the Browser's Back button.<br />
      You should get a "Warning: Page has Expired" error message.</p>

      <p>Time:  <asp:Label id="Label1" runat="server" Font-Bold="True" ForeColor="Red" /></p>

      <asp:Button id="Button1" runat="server" Text="Submit" />

Happy Coding !!

Paging and sorting in sql server

Suppose you have to implement Paging and sorting then following code snippet will help you.

create table #Student(id int identity(1,1), name nvarchar(100), birthdate datetime)
declare @PageSize int=5
declare @MinRowNumber int=1
declare @MaxRowNumber int= @MinRowNumber + @PageSize-1
declare @SortExpression nvarchar(100)='Name' ---'birthdate' Pass here column name.
declare @SortOrder nvarchar(100)='D' --'A' pass here sort order D- for descending and A for ascending.
insert #Student
select 'Viru','1986-12-07'
union all
select 'Sachin','1960-01-31'
union all
select 'Gambhir','1950-06-23'
union all
select 'Shreekant','1983-10-04'
union all
select 'Kapil','1981-03-17'
union all
select 'Yuvi','1986-03-02'
union all
select 'Dhoni','1987-12-05'
union all
select 'Zak','1975-08-17'
union all
select 'Bhajji','2007-08-06'
union all
select 'Ashwin','2010-04-22'
union all
select 'Ojha','2012-02-26'
union all
select 'Ravindra','2012-10-04'
SELECT RowNumber, name, birthdate,id FROM
CASE WHEN @SortExpression = 'Name' AND @SortOrder='D' THEN Name END DESC,
CASE WHEN @SortExpression = 'Name' AND @SortOrder='A' THEN Name END ASC,
CASE WHEN @SortExpression = 'birthdate' AND @SortOrder='D' THEN birthdate END DESC,
CASE WHEN @SortExpression = 'birthdate' AND @SortOrder='A' THEN birthdate END ASC
) AS RowNumber from #Student) AS Student
WHERE RowNumber BETWEEN @MinRowNumber AND @MaxRowNumber
drop table #student

Happy Coding!!

Monday, March 18, 2013

Get users information through active directory

If you have an requirement where you have to read users information from active directory then dot net has provided a dll named "System.DirectoryServices dll ".

Get users information through active directory.

1.You need to add System.DirectoryServices dll reference in your project.

2.Add following code in default.aspx page.
        it automatically finds user name from Page.User.Identity.Name. We have added some properties like: sAMAccountName it only load those properties which we have mentioned in our code.

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.DirectoryServices;
using System.Runtime.InteropServices;
using System.Security.Authentication;
public partial class _Default : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
        SearchResultCollection users;
        string loginUserName = "";
        if (string.IsNullOrEmpty(Page.User.Identity.Name) == false)
            loginUserName = Page.User.Identity.Name.ToString().Substring(Page.User.Identity.Name.ToString().LastIndexOf("\\") + 1);
        using (DirectoryEntry Root = new DirectoryEntry())
            //Establish connection to current loged on users Active Directory
            using (DirectorySearcher Searcher = new DirectorySearcher(Root))
                //Start at the top              
                Searcher.Filter = "(&(objectCategory=person)(anr=" + loginUserName.ToUpper().Trim() + "))";
                Searcher.SearchScope = SearchScope.Subtree;
                //Start at the top and keep drilling down
                //Load User ID
                //Load Display Name
                //Load Users first name
                //Load Users last name
                //Users Distinguished name
                //Ext. Number
                //7D Phone Number
                //Cell Phone Number
                //Cell Phone Number
                Searcher.Sort.PropertyName = "sn";
                //Sort by last name
                Searcher.Sort.Direction = System.DirectoryServices.SortDirection.Ascending;
                users = Searcher.FindAll();
                    //Users contains our searh results
                    //If it's zero then no matches were found
                    if (users.Count > 0)
                        //goes throug each user in the search results
                        foreach (SearchResult User in users)
                           // ResultPropertyCollection rcol = User.Properties;
                            ResultPropertyCollection props = User.Properties;
                            foreach (string prop in props.PropertyNames )
                                ResultPropertyValueCollection values = props[prop];
                                foreach (string val in values)
                                    //if (prop=="mail")
                                    //    Response.Write(val);
                                    Response.Write("<br>"+prop + "= " + val);
                        // Store the DataTable in ViewState.
Active directory can provide a lot of information for a user. I have collected some of information which i required for my task.

Happy Coding!!

Tables without Primary Key in Database

Some times you are analyzing the database to check which tables don't have primary keys then  in that case follwing query will help you to find out the tables:

Below SQL will give you the list of table in you Database not having Primary Keys.
SELECT SCHEMA_NAME(schema_id) AS SchemaName,name AS TableName
FROM sys.tables
ORDER BY SchemaName, TableName;

Happy Coding!! 

Saturday, March 16, 2013

Custom errors in web.config

Some times after hosting web application on the server, we get unexpected error. But we did not get the detailed message for the unexpected error or if we added defaultredirect="error.htm".

<customErrors defaultRedirect="error.htm" mode="On" />

  how can we get detailed message for the unexpected error. Unexpected error may occur on remote or on local server. We can find out exact error message by doing some changes in web.config. Just change Custom error  mode to off.

<customErrors defaultRedirect="error.htm" mode="Off" />
There are three error modes in which an ASP.NET application can work:
1) Off Mode
2) On Mode
3) RemoteOnly Mode

The Error mode attribute determines whether or not an ASP.NET error message is displayed. By default, the mode value is set to "RemoteOnly".

Off Mode

When the error attribute is set to "Off", ASP.NET uses its default error page for both local and remote users in case of an error.

On Mode

In case of "On" Mode, ASP.NET uses user-defined custom error page instead of its default error page for both local and remote users. If a custom error page is not specified, ASP.NET shows the error page describing how to enable remote viewing of errors.


ASP.NET error page is shown only to local users. Remote requests will first check the configuration settings for the custom error page or finally show an IIS error. 

Happy Coding!!