Iteration properties

[libors]

I need regular database exports, which is an iteration over all records.
In my tests, when I create an iterator, records created after the iterator creation are not returned, I have no problem with that.
When I update a record during iteration (insert different value with the same key), sometimes it is not returned by the iterator. I guess this is because it is a different record, the old one is marked as deleted, and the new one behaves as the first case - records after iterator creation are not returned.
Also, it sometimes happens that when I update a record during iteration, the iterator returns both versions of the record with the same key. This I cannot reproduce in my tests, but happens regularly on a production DB with millions of records.
So if I wanted to achieve more consistent results from iteration (no missing updated records or duplicates), am I supposed to stop writing to DB while iterating? Or maybe also pause compaction?