High availability errors

Errors

1. Failed to replicate to SYNC/STRICT_SYNC replica…

Troubleshooting replication failure errors

If you’re writing to the main instance and encounter an error message like “Failed to replicate to SYNC replica ‘instance_1’: replica is not reachable or not in sync with the main”, several issues could be causing this.

The error message identifies exactly which replicas failed, the replication mode (SYNC or STRICT_SYNC), and the specific failure reason. For a full list of possible failure reasons, see the replication errors reference.

Below are common causes and how to resolve them:

1. Network isn’t correctly configured between MAIN and REPLICAs — Check if hostnames/IPs can be reached from the MAIN instance.
2. Replica is behind MAIN — It is possible that the replica is behind MAIN and that the recovery of the replica is in progress. Wait for a bit until the replica catches up with MAIN. If the replica is registered as a SYNC one, the transaction will still get eventually committed.
3. Replica has diverged from MAIN — If the error indicates the replica has diverged, manual recovery or a force sync may be needed. See the force sync documentation.
4. RPC timeout — If the error mentions an RPC timeout, the replica may be overloaded or the network latency is too high. Consider adjusting the deltas_batch_progress_size coordinator setting.