Loadrunner Runtime Settings

Loadrunner Run Time Settings:
When running a training or mentoring session, people often ask what runtime settings they should use; as if there is a magical list of settings that will always be correct for any testing situation. Obviously you select runtime settings that are appropriate for what you are trying to achieve with your test, but the funny thing is that there are actually a small list of settings that are usually appropriate for most situations. Read on…

Whenever I am using a vuser type that allows multiple actions in a single script, I will create a separate action for each business process and put appropriate percentage weightings on each action. It is very unusual to have to do anything more complicated than this. I don’t usually use the “sequential” option or create blocks unless I need to have fractional percentage weightings for a business process – percentages must be integer values, so to run a business process 0.1% of the time you could create a block that runs 1% of the time, and put an action in the block that runs 10% of the time.

It’s also rare to set a script in a scenario to run for a specified number of iterations (mostly done by time or set to run indefinitely). Generally “number of iterations” is only used when running the script in VuGen.

• “As soon as the previous iteration ends” is used when running in VuGen or when loading/verifying data. Do not use this for load testing
• I have never seen the point of the “After the previous iteration ends” option. Why would you want to run an unknown number of transactions per hour against the system?
• Don’t use the “At fixed intervals”. If something causes your users to become “in step”, they will tend to stay that way and continue to all hit the server at the same time.
• “At random intervals” is definitely the way to go. Obviously for your users to create a certain number of orders per hour the iteration time must average to 3600/num iterations in an hour. Do not make the lower boundary value any bigger than the maximum time it takes to complete the business process, or you will end up creating less transactions per hour than you intend to.

• Logging creates additional overhead on your load generators, and can create huge log files.
• I log absolutely everything when debugging in VuGen.
• When running the script as part of a scenario, I leave extended logging on but change the logging to “Send messages only when an error occurs”. This gives a little more information than turning logging off entirely, and won’t create any additional overhead while everything is running smoothly (and if the system is not running smoothly you are going to need to stop the test and investigate anyway).

• Just like the pacing setting, I think that it is a good idea to put some randomness in your think times.
• I use a random percentage of 50-150% of recorded think times.
• Use “Ignore think time” if you are debugging in VuGen or if you are loading/verifying data.

• This option is ignored by most people. It is used to create a parameter with a given value without having to edit the script (as runtime settings can be overridden in the Controller).
• In the screenshot I have created a parameter of ServerName with the address of the test envioronment. If you were testing in more than one test environment at a time, this would make save some time.

• Continue on error is generally only going to be used if you have written code to do something when you encounter an error. Usually the default behaviour of ending the current iteration and then starting the next one is sufficient). I don’t advise anyone to try to write a script that handles errors in the same way as a real user because it will create a lot of additional work for very little benefit, but doing something simple like writing some useful information to the logs and then calling lr_exit(LR_EXIT_ACTION_AND_CONTINUE , LR_FAIL) can be useful.
• “Fail open transactions on lr_error_message” should always be ticked. If you are raising an error, you should fail the transaction step that you are performing.
• “Generate snapshot on error” is useful. If it is a web script, any error messages should be added to your content check rules.
• Run your virtual user as a thread unless you have code that is not threadsafe or there is some other reason to run your virtual users as a process. The overall memory footprint on your load generators will be higher if you run as a process.
• I never use the “Define each action as a transaction” option. If I want a transaction in my script I will add it myself with lr_start_transaction.
• I never use “Define each step as a transaction” either. If it is a web script, I can use the transaction breakdown graph to get this information, otherwise I will add the transactions myself.

• Not all vuser types have this option available.
• Most of the time my virtual users will use the maximum bandwidth.
• If I want to emulate users with bandwidth constraints, I will do this in a separate scenario.
• Google calculator is handy to calculate bitrates if your bitrate is not available from the drop-down list e.g./ “256 Kbps in bps”

All of the following settings only apply to web-based scripts. Each vuser type will have its own runtime setting options. It is important to know what they mean and how they will influence your test results before running any tests that you plan to report on.

• Some people get confused by the User-Agent (browser to be emulated) setting. If 90% of your users use Internet Explorer 6.0 and the rest use Firefox 1.5, you don’t have to change the runtime settings for your users to match this. All it changes is the string that is sent in the “User-Agent” field of your HTTP requests. This is completely pointless unless your application has been written to serve different content to different browsers based on the User-Agent field.
• TODO

• Generally people won’t be using your web applications through your proxy server, so it shouldn’t be part of your test either.
• If you start getting errors that are due a proxy server rather than the system under test, it will just confuse the people who have to fix the problem.
• A proxy server will also make IP-based load balancing ineffective.
• If it’s an intranet application and everyone will be using the application through the company’s proxy, then the proxy server should be explicity declared to be in scope for your load test. You should make sure that you have an identical proxy server for your test environment, or that you have permission to be generating load on a piece of Production infrastructure.

• TODO

• These settings are default values specified by Mercury, rather than being inherited from the web browser that is installed on your workstation. Generally you will not need to change them, but be aware that they are here.

• Download filters are a quick way of preventing your scripts from downloading content from certain URLs or hosts/domains.
• I generally use this feature when the web application in the test environment contains third-party images used for tracking website usage (e.g. images from Webtrends or Red Sheriff etc).
• I think it is better to specify which hosts your script is allowed connect to, rather than which hosts your script can’t connect to (because it’s easy to miss one accidentally, or the application may change and refer to a new third-party domain).
• Use web_add_auto_filter if you want to specify this in your script rather than your runtime settings.

• I have talked about Content Check rules before; I think that if you aren’t using them already, then you are not getting the most out of the LoadRunner feature-set.

Related posts:

1. LoadRunner ContentCheck Rules
2. SOAP over JMS LoadRunner script
3. Scripting Exercise: Unique Usernames
4. Question: Monitoring and alerting with VuGen?
5. New LoadRunner Web (GUI level ) Vuser