Unending log messages about unable to select sync source

Will_Roberts · 2025-01-21T18:33:46.977Z

Hi!

We upgraded our replicasets to MongoDB 6.0.20 last week. Since the upgrade, the logs of some of our secondaries have been filled with lines like this (approximately 160MB/hour):

 {"t":{"$date":"2025-01-21T16:21:04.550+00:00"},"s":"I",  "c":"REPL",     "id":3873113, "ctx":"ReplCoordExtern-22","msg":"Cannot select sync source which is not ahead of me","attr":{"syncSourceCandidate":"other-secondary-mongo:27017","syncSourceCandidateLastAppliedOpTime":{"ts":{"$timestamp":{"t":1737476461,"i":118}},"t":286},"lastOpTimeFetched":{"ts":{"$timestamp":{"t":1737476464,"i":320}},"t":286}}}

This appears to be related to the changes in SERVER-62921 which moved these messages from debug to info.

As far as I can tell, the replicaset is otherwise performing as expected. We have monitoring set up with mongodb.com which is not reporting any replication lag or other concerns. Our applications using the replicaset also appear unaffected.

Is there a configuration issue which could be causing these incessant logs?

The data in the replicaset is very small. I wiped one of the secondaries completely and allowed it to resync as a test, but this did not help.

Any ideas of where to look for a resolution?

Thanks

Ihor_Posliedov · 2025-02-12T15:50:38.517Z

Hello.
We have the same problem and it started right after updating to 6.0.20

Aleksej_Barkhanov · 2025-05-26T21:32:18.491Z

Hello,
Same problem with huge amount of logs “Cannot select sync source which is not ahead of me” after the upgrade. Does anyone solved the problem ?

daniel_scout · 2025-05-27T21:01:13.830Z

Hello, this is still an issue.
The problem occurred because this changed from debug → info. for logging.

i’m still waiting to be allowed to contribute, but if anyone has that ability you can raise a pr yourself:

Screenshot 2025-05-27 at 4.00.38 PM1814×900 167 KB

Aleksej_Barkhanov · 2025-06-02T10:22:58.700Z

Hello,
I found this PR https://jira.mongodb.org/browse/SERVER-102474 with the fix of limitLogFrequency.
Fix is for 8.2.0-rc0 version - waiting for 7.* version to test.