Assessment is not doing an explicit lock anywhere, it is the foreign keys on the cr_items/cr_revisions table that are causing problems. When inserting a new submission, there is a new revision in cr_revisions, which causes the corresponding entry in the cr_items table to be locked.
Despite the fact that i know how a deadlock can appear in general, i am not sure why it happens that often in the assessments package. When 2 users are submitting the same assessment in the same moment, where the questions are in the same order, why would there be a deadlock?
