Broadcom Support attempted for a few more months to answer my questions in the support ticket, but ultimately failed to do so.
My observations follow.
GENERIC_ACTIVITIES_LIMIT has been around for a long time. (The earliest documentation I was able to find is version 11.) This setting limited the number of results displayed in Activities windows in the UC4 Java User Interface (Dialog Client). Here is the relevant excerpt from the v11 documentation:
Depending on the specified filter settings, the Activity Window displays the corresponding tasks. If it contains numerous active tasks, performance is affected negatively because refreshing the Activity Window at short intervals is very CPU-intensive. Therefore, you can limit the maximum number of activities to be displayed using the entry GENERIC_ACTIVITIES_LIMIT. A message in the Activity Window's status line indicates that there are more active tasks than displayed. Limit the Activity Window filter so that non-displayed tasks can also be viewed.
The setting presumably also limited the number of tasks displayed in the Process Monitoring perspective of the Enterprise Control Center (the old name for the AWI). However, the documentation does not state this explicitly.
COMBINED_ACTIVITIES_LIMIT was added in version 12, but the description did not clearly explain how it differed from the existing setting. This note was added below the description of GENERIC_ACTIVITIES_LIMIT, in an apparent attempt to explain how the two settings interacted:
Please note that, in AWI, the number of activities is further restricted by COMBINED_ACTIVITIES_LIMIT. If the value of GENERIC_ACTIVITIES_LIMIT is higher than the value defined in COMBINED_ACTIVITIES_LIMIT, only part of the tasks available for requests on the task list will actually be displayed on the task list.
In version 12.1, a new documentation page was added: List of Tasks. This page was another apparent attempt to clarify the different functions of the two settings. The following excerpt comes the closest to accomplishing this goal:
In AWI, the number of activities is further restricted by COMBINED_ACTIVITIES_LIMIT. If the value of GENERIC_ACTIVITIES_LIMIT is higher than the value defined in COMBINED_ACTIVITIES_LIMIT, only part of the tasks available for requests on the task list will actually be displayed on the task list.
This appears to suggest that if GENERIC_ACTIVITIES_LIMIT is higher than COMBINED_ACTIVITIES_LIMIT, a larger number of tasks than those displayed might be "available for requests." It is unclear how one might perform requests on tasks that are not displayed.
The v21 documentation includes a page called ACTIVITIES_LIMIT parameters that essentially repeats the unclear explanation of the v12.1 documentation.
Several Broadcom staff members have suggested that GENERIC_ACTIVITIES_LIMIT applies to the Automation Engine, while COMBINED_ACTIVITIES_LIMIT applies to the Automic Web Interface (AWI). If this is true, it's hard to see what difference it would make from a user's or administrator's perspective. Regardless of which one is lower, the lower of the two always takes precedence. (If the Automation Engine is capable of sending a larger list of tasks to the AWI than the AWI can handle, a trace of AE→AWI communication might confirm or disprove this.)
It is possible that Broadcom added COMBINED_ACTIVITIES_LIMIT with the intention of providing additional capabilities in the future, such as:
- AWI-side (or even browser-side) filtering
- Actions on the entire list, not just the displayed list
However, neither of these capabilities appears to be present in the product today. Task filters are applied by the Automation Engine, not the AWI, and there are no evident actions one can perform on the whole list of retrieved tasks, rather than on just the displayed list. And obviously, for the AE to send a list of 5000 tasks to the AWI when the AWI can use only 500 of them is a waste of resources.
Given the above observations, it is difficult to imagine any scenario where it would be useful to set different values for the two limits.
The defaults differ by a factor of 10.