Submitting on behalf of a client, who suggests that mdl_task_log should add a nullable adhoctaskid column. The client notes:

"This would make it easier to join to mdl_task_adhoc when troubleshooting. tl.output like concat('%', ta.customdata, '%') only works when the ad-hoc task actually has custom data to match, plus an ID match would be much faster."

This client is on 4.1, and we recognize that any change will be implemented in later supported versions (and they will need to upgrade).