Issue with ultimate thread group and 'generate parent sample' with transaction controllers

[Matthew Tansley]

We've run into an issue on a project where the log entry for a transaction controller in the JMeter results CSV file came back with a very high response time (25+ seconds). This high response time coincides with a few other symptoms:

• The transaction controller has 'generate parent sample' enabled.
• Not all of the requests nested under the transaction controller are being executed.
• The high response time transaction controller log entry happens right at the end of an ultimate thread group 'stage'. 

Our hypothesis:

• When 'generate parent sample' is selected on a transaction controller, JMeter holds the information for each nested HTTP sampler in memory. 
• When threads are 'stopped' at the end of an ultimate thread group step, there may still be some HTTP samplers nested under a transaction controller which have not yet started or are in the middle of making a request. Because the transaction controller is holding the nested HTTP samplers in memory, there is an issue where the transaction controller does not record response time as expected. 

Workaround:

• Our workaround is easy and works for us: we have unticked the 'generate parent sample' option in the transaction controller. 

Overall, this issue is non-urgent, but I'm raising this in case others have faced a similar issue, or if it is a blocker for anyone else.