All publishing and thumbnail conversion is processed using background queues. In a cluster, only one Windchill server processes the queue, using a dedicated MethodServer called the Background MethodServer. As a result, in a clustered environment, all viewable generation is done through the Background MethodServer.

By default, the Thumbnail Generator is executed by the worker on the worker machine, before the viewables are retrieved (along with the thumbnail) by the Worker Agent. However, if this is disabled, and unless you are using remote thumbnail generation, the thumbnail generation is also done from the Background MethodServer, as the Worker Agent runs on the method server that is processing queues.