Monday, December 10, 2007

Performance Testing: Resource Monitoring

What is Load Testing?

The behavior of the application and the utilization of the resources by the application under test is monitored under different load patterns and it is validated against the expected measurements to identify any potential performance errors or bottlenecks.

What is necessity for Monitoring Resources?

Any normal ASP.NET web application will be developed using three tier architecture of Presentation, Business and Data Layers. When a request is made by the client to the server the request is processed by the web server which in turn would be forwarded to the application server and then to the database server. During this processing the System, web server application server and the database server resources are utilized. It is necessary to monitor these resources utilization under load before the application is moved to production in order to identify the performance errors and bottlenecks before it breaks the application and impacts the business of the application.

What Resources need to be monitored?

It is necessary to monitor every logical or physical layer of the web application. In a simple scenario where the application is hosted on a web server and application interacts with the database the sources to be considered for monitoring are System resources, the web server resources and the database resources.It is necessary to identify the specific resources and counters (with their threshold levels) to be monitored at each layer. This identification needs expertise and experience in performance testing. Below is the list of counters that can be used for first level of performance analysis. This table applies for the general ASP.NET applications. However, it needs to be tailored for the specific requirements.

Note: The counters column in the below table to be read as shown in the example: % Processor Time (Processor _Total). Here, the Processor is the Object, % Processor Time is the Counter and _Total is the instance.

How to Monitor the Resources? What tools to use?

On a Windows based machine it is possible to monitor the resources using a utility called perfmon. The same way as perfmon Linux/Unix based machines facilitate the resource monitoring by means of utility known as rstdmon.
Almost every Load Testing tools has integration with Windows Perfmon or has some other has means to provide the facility to monitor the resources. E.g. LoadRunner, Visual Studio 2005 Team Edition for Testers, WebLoad, etc., 


The table of counters provided here provides a possible list of counters that can be monitored for while Load Testing an ASP.NET application. However, it needs to be tailored for specific requirements. For example, while testing a application that uses ADAM process one would be interested to know the processor and memory utilization by the ADAM worker process (dsamain) in specific. It is advised to use the minimum number of high level counters for the first round analysis. Based on the first level analysis one can added more detailed and specific counters for the areas that warrant performance and remove few counters related to areas where the performance seems be good.

-- Lakshminarasimha Mohan

"In god I TRUST, everything else I TEST."

Monday, October 22, 2007

Object Identification Mechanism

QTP identifies the objects by mandatory properties set as default. If the mandatory property values are not sufficient to uniquely identify an object in the Application Under Test (AUT), QTP adds some assistive properties and/or an ordinal identifier in order to create a unique description.

The default Mandatory, Assistive Properties and Ordinal Identifiers can be changed for a specific Class of objects in QTP at Tools -> Object Identification.

The Smart Identification can also be enabled to ensure more comprehensive object identification. The User defined Class of Objects can be mapped to the standard class of Objects so that QTP identifies the user defined objects as standard objects.

What is Smart Identification?

QTP makes use of the special feature Smart Identification when it  fails to identify objects using the defined properties finds an ambiguity in identifying objects. 

The Smart Identification mechanism is more complex and more flexible. If configured logically, a Smart Identification definition can probably help QTP identify an object, if it is present, even when the learned description fails.

The Smart Identification mechanism uses two types of properties, Base Filter Properties and Optional Filter Properties.

Base Filter Properties: The most fundamental properties of a particular test object class; those whose values will not be changed. E.g. html tag = <A> for a object of Link Class

Optional Filter Properties: Other properties that can help identify objects of a particular class.

Smart Identification Process

The QTP follows the below process to identify the objects using Smart Identification Mechanism:

  1. QTP creates a new object candidate list within the Objects Parent Object containing all the objects that match all of the properties defined in the Base Filter Properties list.
  2. New Object Candidate List (OCL) is created by filtering out the objects in the OCL that does not match the first property listed in the Optional Filter Properties list.
  3. The OCL is evaluated in the following manner:
    1. If the new object candidate list still has more than one object, QTP uses the new (smaller) OCL to repeat elimination process for the next optional filter property in the list.
    2. If the new object candidate list is empty, QTP ignores this optional filter property, returns to the previous object candidate list, and repeats the elimination process for the next optional filter property in the list.
    3. If the object candidate list contains exactly one object, then QTP concludes that it has identified the object and performs the statement containing the object.
    4. QTP continues the process described above until it either identifies one object, or runs out of optional filter properties to use.


  • QTP Identifies the Object using the learnt description.
  • If unable to identify the objects using learnt description Smart Identification is invoked.
  • If after completing the Smart Identification elimination process, QTP still cannot identify the object, then QTP uses the learned description plus the ordinal identifier to identify the object.
  • If the combined learned description and ordinal identifier are not sufficient to identify the object, then QTP stops the run session and displays a Run Error message.