For simplicity I ask about a single node. When Mongo iterates a large portion of documents (to answer some query that requires scanning the collection), and requires that all iterated data will be coherent to the same point in time - Does this cause all reads in the iteration to be done under the same storage engine transaction?
if not, what mechanism in Wiredtiger Mongo uses to ensure that:
- older versions of data that are relevant to that point in time won’t be deleted during iteration
- newer versions of the data won’t be seen by the iteration