Pacing Calculation in Loadrunner - Performance Testing

What is Pacing?

• Pacing is the time interval between the iterations. 
• It ensures better gap between the user sessions in the load test.
• It is needed to achieve the required TPS in the load test. 
• Ignoring the pacing will flood the server with requests continuously thus making the test inappropriate.

Pacing can be set in the Run Time Settings.

1. As soon as the previous iteration ends

New iteration will start as soon as the previous iteration ends. Which means Pacing = 0.

2. After the previous iteration ends - with

New iteration will start at fixed or random delay after the previous iteration ends.

Fixed - Mention the exact delay in seconds.

Random - Mention the min and max delay in seconds and pacing will be selected between the specified range.

Example: Pacing = 60 Seconds and Time taken for 1 iteration = 50 seconds.

So the First iteration will end at 50 secs and Second iteration will start after 60 secs from the end of first iteration. Since Pacing = 60 secs.

Here pacing acts as a wait timer.

3. At Fixed or Random intervals - every

Here the Pacing timer for the new iteration will begin when the previous iteration starts and the iterations will be fired at the exact timer. In this case Pacing time should be higher than the Time taken for 1 iteration or else the second iteration will start right after the end of the first iteration.

Fixed - Mention the exact delay in seconds.

Random - Mention the min and max delay in seconds and pacing will be selected between the specified range.

Example 1 : Pacing = 60 Seconds and Time taken for 1 iteration = 50 seconds.

Pacing timer will start with the iteration. First iteration will end at 50 secs and after which there will be 10 secs gap after which the second iteration will start.

Example 2 : Pacing = 60 Seconds and Time taken for 1 iteration = 70 seconds.

Pacing timer will start with the iteration. First iteration will end at 70 secs and after which there will be no gap since the Time taken for 1 iteration has surpassed the pacing time. So the second iteration will start immediately.

Here pacing just acts as a timer.

Formulas to calculate Pacing

Formula 1:

P = ( D - ( I * Ti ) ) / ( I - 1)

where

P   = Pacing time in secs
D  = Duration of the test in secs
I   = No. of Iterations
Ti = Time taken for 1 Iteration in secs

Formula 2:

simplified form of formula 1

P = D / I

where

P   = Pacing time in secs
D  = Duration of the test in secs
I   = No. of Iterations

Formula 3:

P = ( V * D) / Ts

where

P   = Pacing time in secs
V = No. of users in the script for which pacing is calculated
D  = Duration of the test in secs
Ts = Total no of Transactions to be achieved in the test for the script, for which pacing is calculated