Hi guys,
we’re facing very strange error. Long story short - we’ve really old database on mongo 3.4.
Finally we have the time and resources to start upgrading the same as much as we can. However, to avoid downtime, we decided to go the long path and do upgrades version by version.
No issues with 3.4->3.6, 3.6->4.0 (after each upgrade we did setFeatureCompatibilityVersion to the respective version). However, once we switched to 4.2 and tried to setFeatureCompatibilityVersion we get an error
BSON field 'setFCV-find-matching-sessions.lastWriteOpTime is missing but a required field`.
It took us some time to find out what exactly is the problem, but finally our best guess are 2 records in config.transactions`` collection. All records, except those two, have lastWriteOpTime field, while those two havelastWriteOpTimeTs` field (rest don’t). But those transactions seems “stucked”. No progress and transaction reaper doesn’t abort them.
Any suggestions how we can proceed and fix this so that we can continue with the upgrade?