> Our most recent report on MongoDB 3.6.4 focused on causal consistency and linearizability in sharded collections. We found that sharded clusters appeared to offer linearizable reads, writes, and compare-and-set operations against single documents, so long as users ran with read concern linearizable and write concern majority. However, any weaker level of write concern resulted in the loss of committed writes. MongoDB’s default level of write concern was (and remains) acknowledgement by a single node, which means MongoDB may lose data by default. Although the write concern documentation does not make this clear, the rollback documentation states:
This was prior to the introduction of transactions years ago. The versions stated in your comment are past EOL and not offered in Atlas today. Not relevant to today's reality.
