Question

In my Windows application I try to connect to SQL Server 2008 with following code:

SqlConnection connection = new SqlConnection(Properties.Settings.Default.KargarBandarConnectionString);
SqlCommand command = new SqlCommand("Select IsAdmin from Users where UserName=@UserName And Password=@Password", connection);
SqlDataReader dataReader = null;

command.Parameters.AddWithValue("@UserName", UserNameTextBox.Text.Trim());
command.Parameters.AddWithValue("@Password", PasswordTextBox.Text);
try
{
    connection.Open();
    dataReader = command.ExecuteReader();

    if (dataReader.HasRows)
    {
        while (dataReader.Read())
        {
            IsAdmin = dataReader.GetBoolean(0);
        }
        this.DialogResult = DialogResult.OK;
    }
    else
    {
       FMessageBox.ShowWarning("error");
        UserNameTextBox.Focus();
    }
}
catch (Exception ex)
{
    if (progressForm != null)
        progressForm.Close();

    FMessageBox.ShowError(ex.Message);
}
finally
{
    if (dataReader != null)
    {
        dataReader.Close();
        dataReader.Dispose();
    }
    if (connection != null)
    {
        connection.Close();
        connection.Dispose();
    }
}

Everything works properly, but sometimes I get the following error:

timeout expired. the timeout period elapsed prior to obtaining a
connection from the pool …

How can this be solved?

Answer 1

The reason you’re getting this exception is because you have exhausted your connection pool and the number of “available” connections in your application.

Every time you open a connection, one is pulled from the connection pool if possible, or a new one is created if not.

However, to prevent galloping usage of connections, a limit of 100 (I think this is configurable) exists, and if you try to use more than 100 simultaneous connections, the code will not create new ones, and instead sit down to wait for one to be returned to the pool, and in this case you get a timeout if it sits too long.

So, for the particular example of code you’ve shown, I would:

Close the connection before I show an error messages to the user

However, unless 100 users are seeing the error message and leaving it there at the same time, it is unlikely the code you’ve shown is the cause of this problem.

Other than that, I would go through the entire application and ensure you don’t have any connection leaks other places.

This particular type of exception can occur in one spot even though the problem is somewhere else. Example: A report is leaking an open connection every time it runs, and you run it 100 times successfully, then someone tries to log in, and the exception occurs in the login form.