Jmeter Scripting Essentials
Common best practices & approaches to
keep your jmeter script in shape

Anton Serputko
Staff Performance Engineer at ServiceNow
Performance testing:
- community: t.me/perforator_club
- events: youtube.com/@serputko
- trainings, outsourcing, consulting: perforator.me/
Linkedin: linkedin.com/in/serputkoa/

Performance testing and
Jmeter in 40 mins?

No, it’s tips for you to
start using in your work
with Jmeter

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Source of knowledge
1. Jmeter documentation
2. Blazemeter knowledgebase
3. Stackoverflow
4. Past experience
5. Performance community

What is good Jmeter scenario
1. realistic production-like user flow and load profiles
2. correlation and parameterization
3. handling static data
4. maintainability
5. performance
6. test metrics results gathering

Test results gathering

Instead of

Get this

Test results in influxdb and grafana
1. Get real-time data
2. Extensive monitoring and analysis
3. Test results comparison
4. Configure backend listener props to get
valid results!
5. Contact me to get dashboards

Backend Listener configuration
1. application: ${__TestPlanName}@${__time(yyyy-MM-dd'T'hh:mm:ss,)}
2. test title: ${__P(CUSTOM_INFO,default value)} in application and
3. eventTags: users=1,rampup=,...
4. percentiles: 90;95;99;50
5. summaryOnly: false

Get valid results
quick fix without going too deep in details
edit jmeter.properties file
1. backend_metrics_window_mode=fixed -> timed
2. increase window sizes to 100000

Scenario structure
1. keep scripting style
a. variable naming convention
b. elements location
c. elements naming convention
2. be careful while recording
3. keep scenario logical using Logic
controllers
4. control load profile(% of actions
execution and think times)
5. debug and validate
6. re-use elements if needed

Elements naming
1. name all elements(pre/post processors)
2. do not parameterize name of sampler with ${}
3. replace parameterized value with static value in name
4. add method/details to recorded request url if they have similar
naming
5. name requests for API testing like GET /v1/auth/login

Elements scope
Be sure element is located where you expect

Scenario recording

Static data
Be default:
1. exclude “All suggested excludes” in Http test script
recorder
2. remove all hardcoded static data from the scenario
3. enable retrieve all embedded resources and parallel
downloads
a. use cache manager if retrieving static data
b. use 6 parallel downloads to
c. disable when you understand possible affect

3-d party resources
1. remove from scenario
2. when 3-d party could be left
a. not sure about their performance and it’s not async
b. use sandboxes or contact service providers
3. mock them if 3d party response is required for the flow
3d party examples: Google analytics, Google AdSense, Paypal, UPS shipping,
Browser internal tracking

Using recorder
1. filtering
a. better to leave extra then leave less
b. ask devs/check api docs if not sure
2. requests grouping with transaction
controllers
3. remove toggled redirect requests
4. always think if what you see is logical:
request duplication, extra requests, etc
5. keep recording action as realistic as
possible, pay attention to actions which
triggers ajax requests

Auto replace while recording
a. auto replace variables while recording if User defined variables is in scope of recorder
i. use with caution as more data could be replaced then you expect
b. auto replace with http request defaults to change to blank

Before scripting
Before scripting:
1. analyze logs, analytics, APM statistics from prod
2. define load profile
a. think times between actions
b. requests, actions percent distribution
c. scenario logic: loops, ifs, etc

While scripting
1. keep scenario logic realistic with logic controllers
a. use built-in jmeter components if possible
b. avoid overcomplicating scenario
c. avoid using custom JSR223 scripting when possible
2. add think time to the scenario:
a. Timers in Flow control action between transaction
controllers
3. control % of action execution
a. Throughput controller
b. Weighted switch controller
c. ALWAYS validate percentage distribution when using
throughput/weighted switch controllers on dummy samples
d. Do not use multiple thread groups
4. cover client logic. Extra requests for logged in user, etc
5. use assertions only in key places to reduce overhead

After scripting
1. validate your scenario
2. compare you test result profile with production profile, and adjust if
needed

Non-linear/Custom logic
1. If/While controller:
a. use groovy functions for best performance
b. do NOT use JS in any case
c. do not forget about .toInteger() for numbers
d. check positive and negative flow
2. Parallel controller
a. new connection and internal thread is created
in for each request
3. Weighted switch controller
a. save values by switching focus to another field

JSR223 Elements
1. Use groovy as a must!
a. a lot of solutions on stackoverflow using beanshell
beanshell is compatible with groovy
b. avoid using JS in any case!
2. Use .setIgnore() for JSR223 sampler
3. Use log.info(“{}”,var), out.println to debug groovy scripts
4. Do not use ${} in groovy, use vars.get()
5. Do not use ${VAR}, ${__JmeterFunction()} as they will be
cached
6. do not forget about .toInteger() in comparison
7. choose “cache compiled script if available” option

Scenario parameterization
1. what if scenario is not parameterized
a. will not work on different env
b. data is hardcoded so hitting cache
c. auth will expire after some time
2. types of parameterization
a. static values parameterization- variables
b. requests correlation- post processors
c. user input parameterization- jmeter functions
3. prefer dynamic data over reading from csv files

Variables
1. naming conventions
a. a, var, ProductID, productid - bad
b. PRODUCT_ID, productId - good
2. use User Defined Variables for variables creation
a. use Jmeter properties in variable value
b. variable could be created in Test Plan, but don’t do that
3. use jmeter properties to pass parameters from command line
4. CSV file to get data
a. use csv only for static data like user credentials
b. avoid using dynamic data which frequently changes, use
post processors to get data from server responses
c. use relative path using get base directory + separator
groovy function
d. use just file name if csv is located near jmx

Post processors/extractors
1. Correlating transactions
a. usually requests are dependent from each other, data sent by the client was previously
received from server
b. get data from responses using regex, jsonpath, css selector, boundary and xpath
c. usually no need to parameterize 100% of parameters
i. for example no need to parameterize amount of products on add to cart request
2. use multiple variables using regular expression groups from single extractor
3. use regex, jsonpath tester in view results tree to debug queries
4. set NOT_FOUND default value in extractors
5. do not place regex extractor on transaction controller level as it applies to multiple requests

Jmeter functions
● install Jmeter custom plugins
● use function helper
● re-use jmeter function result as a variable
● if function is used in user defined variables it will be initialized
only 1 time and then not changed when you call the variable

Debugging
1. add 1 debug post-processor on test plan level
a. avoid adding many debug samplers/post-processors
2. validate jmeter errors in jmeter.log
3. common issues with scope: wrong placement, not in element
4. if you put function call in user defined variables it will be initialized
inly 1 time and then not changed when you call the variable
5. validate positive and negative cases for if controllers
6. use log.info(“{}”,var), out.println to debug groovy scripts
7. debug issues/validate logic with dummy sampler
8. common issues working with variables:
a. misspelled ${} with $(), $[], {} without $, etc.
b. misspelled variable name on create or use
c. [ ] space before/after VARIABLE_NAME

Re-using elements
1. module controllers. re-use ONLY really
frequently used actions
2. do not move everything to module
controllers thoughtlessly
a. harder to navigate through scenario
3. if re-usable element is moved the link in
module controller will be broken

Non gui mode
● startup command and parameters
● generate html report
● write results to csv
● set jmeter properties to parameterize scenario
● write to log
● console status logger
● validate jmeter errors in jmeter.log
● run tests in non-gui mode
● parameterize non-gui run with jmeter properties

Jmeter plugins
● plugins in plugin manager might be outdated
● webdriver support plugin was not supporting
headless but github master had this changes
● check for bugs and read documentation(sometimes
several times)
● weighted switch
● parallel controller

Undo/Redo

Modify undo.history.size=0 in jmeter.properties

Use backups

Thank You
Let’s keep in touch: linkedin.com/in/serputkoa/
Join our performance testing:
- community: t.me/perforator_club
- events: youtube.com/@serputko
- trainings, outsourcing, consulting: perforator.me/