We have seen a few customer's reporting negative impacts in performance when initiating A/B testing in their DXP environments. This can often be first noticed when working in a production environment if not thoroughly tested in lower environments, and can result in the site being potentially brought down. The exact source of the behavior could be triggered by inefficient code being called, a bug within the package, or any number of other sources.
When there is a dip in performance for a site leveraging the EPiServer.Marketing.Testing package it is important to disable the testing feature within Config > Tool Settings > AB Testing Configuration. Disabling the feature is normally enough to temporarily relieve performance issues relating to the package, but in some circumstances a webapp restart might be needed.
After disabling the jobs on an environment make sure that the site is on the latest release of the EPiServer.Marketing.Testing package. Engineering releases patches regularly to the package to resolve known bugs, so being on the latest release for the EPiServer.Marketing.Testing is normally advised by engineering.
Once the site is confirmed to be on the latest release it is important to run testing both on the uncompiled development site that deploys into the DXP platform, and on the non-production environments such as Integration and Preproduction.
In the event that upgrading the EPiServer.Marketing.Testing package does not resolve the behavior and the performance dip is noted to be exclusive to the DXP environment our engineering team may request access to the site's uncompiled code for review or further access to non-production environments for testing.