Automating test data generation in Performance testing-Jmeter -

kindly suggest automating test data generation in jmeter performance testing or not? if have generate test data in large numbers, impact performance testing in negative manner? example: if have generate username, email id in large numbers , fetch them in script using function , random variable,will jmeter consume more time fetching process , affect response time results? kindly suggest pron's , con's of automating test data generation in performance testing?

as long generated data fits java heap fine generate test data on-the-fly.

there should not impact on response time pre/post processors , timers duration not being counted (unless have transaction controller in generate parent sample mode)

make sure following recommendations 9 easy solutions jmeter load test “out of memory” failure guide of jmeter instance(s).