As elaborated in PYTHON-1668, it turns out that if I set write_concern or read_concern for the db or collection handles, they will be silently ignored.

If I understand the background to this situation correctly: A transaction can mix several db and coll handles in a single transaction. They can have different write_concerns and read_concerns, yet the transaction obviously can only have one and the same, as those are properties of a transaction. The solution is to silently ignore those settings for db and coll objects inside a transaction.

For users who won't read the documentation, this is not obvious and I fear many will not get the durability and consistency they expected. (Just like I didn't.) This is essentially a data corruption bug - even if a UX kind of that.

I would suggest the following instead:

db and coll objects inside a transaction MUST have write_concern and read_concern set to either:

• defaults/unset
• matching those of the transaction
• if neither of the above, raise an error