'Issue with Arbiter feature compatibility after upgrade of replica set of two nodes with Arbiter to 3.6

I have upgraded MongoDB replica set to 3.6 following this instruction https://docs.mongodb.com/manual/release-notes/3.6-upgrade-replica-set/. When I executed command

db.adminCommand( { setFeatureCompatibilityVersion: "3.6" } )

both Primary and Secondary updated feature compatibility to 3.6, but Arbiter feature compatibility remained 3.4.

Why it remained 3.4 and how to make Arbiter have same feature compatibility as Primary as Secondary?

mongodb


Solution 1:[1]

From MongoDB 3.6.7 arbiters continuously log "Using sessions while not fully upgraded to FCV3.6" even though replset is FCV3.6:

Arbiters always have the downgrade value of FCV, regardless of the FCV of the replica set. So if the arbiter has binary version 3.6, it will always have FCV=3.4. They never learn the FCV, since they do not replicate the admin.system.version collection. Arbiters' behavior is not allowed to depend on FCV for this reason.

Solution 2:[2]

This thread has enough latest information:

https://www.mongodb.com/community/forums/t/fcv-is-automatically-advanced-to-4-4-on-arbiter-after-upgrading-replica-set-from-4-2-on-windows/159863

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 snak
Solution 2 satya

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