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MongoDB · Database Server & Atlas
MongoDB server reported: Unknown Repl Write Concern.
Quick Answer
Error code 79 on your MongoDB Database Server & Atlas means: MongoDB server reported: Unknown Repl Write Concern.. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
MONGO-ATLAS-DEDICATEDMONGO-ATLAS-SERVERLESSMONGO-COMM-6.0MONGO-COMM-7.0MONGO-COMM-8.0MONGO-ENT-6.0MONGO-ENT-7.0MONGO-ENT-8.0
Likely Causes
  1. MongoDB returned code 79 (UnknownReplWriteConcern) while processing this request path.
  2. Replication or sharding state was not aligned with the operation preconditions.
  3. Node role/configuration changed between targeting and execution.
How to Fix It
1
Review logs/telemetry for code 79 (UnknownReplWriteConcern) and capture the exact command and parameters that triggered it.
2
Refresh topology metadata and retarget the command using current primary/shard ownership.
3
Review replication/sharding events around the timestamp to confirm role transitions.
4
Gate retries on a stable cluster view and avoid stale routing caches.
5
Add monitoring for recurring UnknownReplWriteConcern events so future incidents are detected and triaged faster.
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Related Error Codes
12456
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