There is much amusement to be obtained from reading Jepsen's report: "MongoDB’s default level of write concern was (and remains) acknowledgement by a single no

There is much amusement to be obtained from reading Jepsen's report: "MongoDB’s default level of write concern was (and remains) acknowledgement by a single node, which means MongoDB may lose data by default. ...Similarly, MongoDB’s default level of read concern allows aborted reads: readers can observe state that is not fully committed, and could be discarded in the future. As the read isolation consistency docs note, “Read uncommitted is the default isolation level”. We found that due to these weak defaults, MongoDB’s causal sessions did not preserve causal consistency by default: users needed to specify both write and read concern majority (or higher) to actually get causal consistency. MongoDB closed the issue, saying it was working as designed" http://jepsen.io/analyses/mongodb-4.2.6 http://jepsen.io/analyses/mongodb-4.2.6