Is the objectid column on the archive_object12_5 table equivalent to the tasksessionid on the archive_tasksession12_5 table?
Yes, The Object table is used to store the serialized events and tasksessions. The objectid and objecttype are combined primary keys. The objectid is the guid of current tasksession or event. The objecttype indicates whether the object is a tasksession (objecttype=1) or event (objecttype=2). For archive database, each row in archive_object12_5 corresponds to a row in either archive_tasksession12_5 or archive_event12_5.