C# .NET - Exception filters and extendable stored procedures

what are exception filters ? what is the use of them? what is the use of extendable stored procedures? 

why should not we  re throw the ex; why should we need to preserve the original call stack? for what purpose?

try 
{
}
catch( exception ex)
{
 throw ex;

}

Hi,
exception filters:-

Exception filters allow you to specify a conditional clause for each catch block.  Instead of a catch block handling all exceptions of a specific type, they allow us to write catch blocks that handle exceptions of a specific type (or all exceptions) only when a certain condition is true.  For example, consider the following Visual Basic .NET code:

Try
        ' do something that could throw an exception
Catch e As FileNotFoundException When MyFilterMethod(e)
      Console.WriteLine(“first“)
Catch e As FileNotFoundException When MyFilterMethod2(e)
      Console.WriteLine(“second“)
Catch e As FileNotFoundException When MyFilterMethod3(e)
      Console.WriteLine(“third“)
Catch e As DivideByZeroException
    Console.WriteLine(“fourth“)
End Try

use of extendable stored procedures:-

Extended stored procedures are a very powerful way to extend the functionality of SQL Server. The following excerpt is from the SQL Server Books Online: You must treat the extended stored procedure DLL as any other DLL development: It is shared code, and multiple threads can access it at the same time. As with any production-worthy project, make sure to use thorough design and complete testing.

For re throw :- you havnt handled the exception fully in your policy, but as you have caught it, the exception no longer exists so rethrowing it just makes sure it will ripple up the stack.if youdont rethrow it you will simply cause the exception to disappear.

hope it helps you.