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I want to add new servers to my replica set. So I used rs.add("<IP>:<PORT>") to add the servers. But the servers became not reachable. On checking Logs I found out it was feature compatibility version issue. So I updated the feature Compatibility Version using, db.adminCommand({ setFeatureCompatibilityVersion: "3.6" }). But on checking status I got,

rspp1:PRIMARY> db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
{
        "featureCompatibilityVersion" : {
                "version" : "3.4",
                "targetVersion" : "3.6"
        },
        "ok" : 1,
        "$gleStats" : {
                "lastOpTime" : {
                        "ts" : Timestamp(1681888293, 1),
                        "t" : NumberLong(27)
                },
                "electionId" : ObjectId("7fffffff000000000000001b")
        },
        "$configServerState" : {
                "opTime" : {
                        "ts" : Timestamp(1681889207, 1),
                        "t" : NumberLong(5)
                }
        }
}

. This means for some reason my upgrade is stuck and not finished. I need a way to revert it back to 3.4. Also db.adminCommand({ setFeatureCompatibilityVersion: "3.4" }) doesn’t work because the first upgrade is not completed yet. I want ot stop the update and revert it back to 3.4 Kindly help me.

I tried db.adminCommand({ setFeatureCompatibilityVersion: "3.6" }). I was expecting { "ok": 1 }

Chirag Sharma
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  • How did you update? Did you follow [Upgrade a Replica Set to 3.6](https://www.mongodb.com/docs/manual/release-notes/3.6-upgrade-replica-set/)? Just a note, the same page also provides [Downgrade 3.6 Replica Set to 3.4](https://www.mongodb.com/docs/manual/release-notes/3.6-downgrade-replica-set/) – Wernfried Domscheit Apr 19 '23 at 10:31
  • I can't downgrade it because the previous upgrade is stuck. It's not completed yet. how can I complete or kill it? – Chirag Sharma Apr 19 '23 at 10:51
  • Again, did you follow the procedure. An upgrade may take several hours (without causing any problem) And what do you mean by "I found out it was feature compatibility version issue"? What is the error message? – Wernfried Domscheit Apr 19 '23 at 11:56
  • The error looke like, "2023-04-14T10:06:19.718+0200 F STORAGE [initandlisten] Unable to start up mongod due to missing featureCompatibilityVersion document." this error was found in the logs file of the server that I added in the replica set. I did follow the procedure nad it's been 4 days. I don't know what's wrong with this. – Chirag Sharma Apr 19 '23 at 12:17
  • What is the actual version of the `mongod` binaries? Did you mix any? – Wernfried Domscheit Apr 19 '23 at 13:08
  • I'm not aware of how can I see that. But the server version is 3.6.23 and Feature compatibility version was 3.4 and then I upgraded it to 3.6 which is where it's stuck. – Chirag Sharma Apr 20 '23 at 07:58
  • Use `mongod --verison` to get it. – Wernfried Domscheit Apr 20 '23 at 08:58

0 Answers0