I want to extend my previous issue #20388 about transaction in Attachment. There is second case, then we can have a problem. We can save file on disk, but rollback a transaction with creation of Attachment record. In this case we obtain ghost files without link with Attachment. In long term it leads to pollution of file storage.
I fix this situation on one of my plugin by "follows way:":https://github.com/Loriowar/redmine_conceptual_attachments/blob/master/lib/redmine_conceptual_attachments/attachment_patch.rb#L10

after_rollback :delete_from_disk, on: :create

Hope, this can be useful for Redmine.