I’m Dan Pasette, Executive Vice President of Core Engineering at MongoDB. I'd like to thank aphyr for posting the detailed report on MongoDB 4.2.6. We were able to use these findings to identify a bug that can lead to a previously committed transaction being incorrectly retried in the presence of a primary failover and a subsequent transaction commit retry. From our testing, this bug is the cause of the anomalies described in sections 3.4 - 3.7 of the report.
This bug has been fixed and backported, and will be available to users in MongoDB 4.2.8 onwards. The MongoDB test suite has been updated to ensure that this specific phenomenon is detected in future releases. We are also planning to update the version of Jepsen we are currently running in our CI loop to include the newest test case used in the report.
Last, we’ve made some changes to how we share information discussed in the Jepsen reports on our website. You can find the updated page here (https://www.mongodb.com/jepsen).
A detailed description of the bug can be found here: https://jira.mongodb.org/browse/SERVER-48307
This bug has been fixed and backported, and will be available to users in MongoDB 4.2.8 onwards. The MongoDB test suite has been updated to ensure that this specific phenomenon is detected in future releases. We are also planning to update the version of Jepsen we are currently running in our CI loop to include the newest test case used in the report.
Last, we’ve made some changes to how we share information discussed in the Jepsen reports on our website. You can find the updated page here (https://www.mongodb.com/jepsen).