My understanding is that the ACT_RU tables are populated with in flight processes and they are moved to ACT_HI tables once the process is done. But For some reason, I can not see the records for in flight processes in ACT_RU tables, though I can see them in the history tables once the process is complete. Below is the configuration extract
Data is only committed to the ru tables if you have a waitstate (e.g. a usertask). If you do not have these, the ru tables will never be populated and data only shows up in the hi tables