Required Load Generator Calculator

PerfMatrix Site Link: https://www.perfmatrix.com/load-generator-calculator/

Theoretically, the more complex a protocol scripting, the more consumption of system resources. It is a common question "How many Load Injectors require for my load test?" HP has developed the Protocol Complexity Matrix to visualize this.

In one of the LoadRunner community article, I found a piece of article which stressed over to calculate no. of VUsers on one load injectors rather than go blindly on your assumption.

"In previous versions of LoadRunner and Performance Center, a protocol footprint spreadsheet was distributed by HP to provide a guideline for how much memory a script of a particular protocol would consume.  The problem was recipients of the footprint spreadsheet thought of it as definitive rather than prescriptive. It is much better to use a repeatable process and a formula to mathematically estimate the total number of users a load generator can run on a per-script basis."

I typically apply a simple method to get how much VUsers can be run on one LG. First prepare load scenario with 1 user and 1 LG, also provide a long run duration (let's say 2 hours). After starting the test, gradually increasing the number of Vusers by adding from the run window of the test. In parallel, monitor the host resource graphs. Once host resources (CPU/Memory) reach the highest value, stop the test and get the number of VUsers on 1 host. But this method can not be recommended because you can not determine the true capacity of LG using the above method. It is helpful to get approx value.

The method recommended by HP is based on the formula in which below inputs are required.

1. First VUser Memory: To determine “First VUser Memory”, create a load test using the script that you want to examine with 1 Vuser and execute the test. Open host resource graph (Memory) and note down the available MB of RAM. Now start your test. Make sure you start your test with some delay so that you can get load generator available memory. Once VUser starts you can see the decrease in available memory. This is the “First VUser Memory”.

2. Each Additional VUser Memory: Run the same test for 5 Vusers. Keep the same delay at the start and have each user start one minute apart.  Monitor the load generators available MB of RAM and note the drop in free RAM space as each user starts.  Average the amount of RAM that the second virtual user on up uses and this is the “Each Additional VUser Memory”

3. Total LG RAM: Determine the total RAM on the load generator.

4. LG RAM used by OS: Determine the RAM used by Operating System on the load generator.

How do I check RAM usage on my PC?

• Right click on Task Bar of LG
• Left click on “Start Task Manager”
• You will see “Windows Task Manager” window
• Click on “Performance” tab within “Windows Task Manager”
• “Total” under Physical Memory; which in this case is 2047MB or 2GB.
• “Memory” Section shows the amount of Memory computer is currently using; which in this case is 1.13GB. Make sure your LG should be idle so that you can correctly calculate the memory consumed by OS.

Calculate VUsers on 1 Load Generator:

First VUser Memory (in MB) = 
Each Additional VUser Memory (MB) = 
Total LG RAM (in MB) = 
LG RAM used by OS (in MB) = 
 No. of VUsers on 1 LG = 

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Calculate Required no. of LG for your test:

Total number of VUser in your Test = 
VUsers on 1 LG (from above Calculator) = 
 No. of LG(s) required =  (round-off the value to the higher side)

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Reference: https://community.hpe.com/t5/LoadRunner-and-Performance/The-Protocol-Complexity-Matrix-and-what-it-means-for-your-load/ba-p/6559424#.WD5qobJ96Uk

Related Topic:

• No. of VUsers (Threads) Calculator
• Think Time Calculator
• TPS Calculator
• Pacing Calculator