There is also one more level of horror people often forget. Sometimes the history unwinds itself. Some outages will require restoration from a backup and some a

There is also one more level of horror people often forget. Sometimes the history unwinds itself. Some outages will require restoration from a backup and some amount of transactions may be lost. It does not happen often, but it may happen. Such situations may lead to e.g. sequentially allocated IDs being reused or originally valid pointers to records now point nowhere and so on.