Create a new column for tp_comment_id in tp_feed_entry_linked_obj Drop uniqueness constraint on (tp_feed_entry_id, object_set_key, object_type, object_id) FK from tp_feed_entry_linked_obj.tp_feed_entry_id to tp_feed_entry.id. Index for tp_feed_entry_linked_obj.tp_feed_entry.id. FK from tp_feed_entry_linked_obj.tp_comment_id to tp_comment.id. Index for tp_feed_entry_linked_obj.tp_comment_id.