Showing posts from February, 2012

PSR Tool in Windows 7

PSR Tool in Windows 7 Many people are not aware about an amazing tool included in Windows 7 .  The tool is called Problems Steps Recorder.  Before you start a flow, start the PSR and it will take screen shots every time the mouse clicks on the screen and will keep a log of what happened when the mouse button clicked.  After you are done running the flow, stop the PSR and save the file.  If you have a defect, you can send this to dev team and then they will not bug you to reproduce.  This will save precious time!! Also this tool can give good solution for KT sessions, defects, user guides or any other area that requires step by step description and screenshots (and you don’t need to do anything, just to run the flow or perform the activity) 1.        In Windows 7 , click start menu and type “psr” 2.        When psr.exe shown up on menu, click on it to open 3.        This will open: 4.        Click on the arrow at the very right side and click settings. 5
Little's Law : If we consider customers C arriving at a rate R to the server and spending T time utilizing the server, we can say that C=R*T. This is known as Little’s Law. For a given system the throughput of a system can be measured by dividing the number of users with the time spent in the box (R=C/T). Now let’s assume that users will wait a To time in between requests, which we know as a think time. This is an interval typical for users to interact with the system. So from the C=R*T we can expand and infer that the number of users in think time will be Co=R*To. But the number total of users in such a case will be CTotal = C+Co = R*T + R*To = R(T+To). So CTotal = R(T+To). R=C/(T+To) where T is time spent in the Server(response time), To is the average think time,   C number of users and R the throughput.       If we had a system with 200 users requesting services with 1600 request for 15 minutes and response time average of 2 seconds we can characterize
Little's Law - To Get Concurrent Number of Users   One of the basic queuing theory principles applied in Software Performance Engineering is Little's law (a). It states that the total number of users in the system is equal to the product of throughput and response time. Total Number of Users = Throughput X Response Time While calibrating your load test runs, one should always cross check the test results (throughput, response time, user-load simulated) to identify whether the load generator nodes themselves are not becoming the bottleneck in the system. From performance test results we can easily calculate the concurrency for a particular transaction using Little’s Law. Little’s law allows us to relate the mean number of items in the system in our case concurrent users with the mean time in the system (response time) as follows: Number of Items in the system = Arrival Rate x Response Time Rule to remember before you use little law you must make

What is the difference between a process and a thread?

Process is defined as the virtual address space and the control information necessary for the execution of a program while Threads are a way for a program to split itself into two or more simultaneously running tasks. In general, a thread is contained inside a process and different threads in the same process share some resources while different processes do not. In terms of Loadrunner: Running as Process: - When we run Vuser as a process, LoadRunner creates 1 process called mmdrv.exe per Vuser. So if we have 10 Vusers, we will have 10 mmdrv.exe processes on our machines. - If you run each Vuser as a process, then the same driver program ( such as mdrv.exe or r3vuser.exe) is launched (and loaded) into the memory again and again for every instance of the Vuser. - Loading the same driver program into memory uses up large amounts of RAM (random access memory) and other system resources. This limits the numbers of Vusers that can be run on any load generator. -Disables MultiThreadi