Performance degradation is witnessed in Appian 17.4 and later. The engine_call_details.csv log also shows that the number of 'getUser' calls have significantly increased.
A bug in the parallel evaluation of expressions introduced additional calls to the personalization (PE) engine, causing the engine to have high CPU utilization. This issue has been addressed via AN-102147 in the following hotfixes/versions:
Apply the latest hotfix to your Appian installation or upgrade to the latest version of Appian.
This article applies to Appian versions 17.4 and 18.1.
Last Reviewed: August 2018