MSDN Community – Replication Troubleshooting

Overview

Replication ensures that data across multiple databases or services stays synchronized. When replication fails, it can lead to data inconsistencies, performance degradation, and application errors. This guide walks you through the most frequent problems, diagnostic tools, and remediation steps.

Common Issues

Latency & Lag

High latency between primary and replica causes replication lag.

# Example: Check replication lag (SQL Server)
SELECT
    replica_server_name,
    replication_latency = DATEDIFF(SECOND, last_commit_time, GETUTCDATE())
FROM sys.dm_hadr_database_replica_states
WHERE is_primary_replica = 0;
Conflict Errors

Conflicts arise when concurrent updates occur on multiple replicas.

# Example: Resolve conflict in MongoDB
db.getSiblingDB('mydb').runCommand({
   resolveConflict: "myCollection",
   conflictId: ObjectId("654321abcdef0123456789ab")
});
Configuration Mismatch

Inconsistent schema or settings between source and target cause replication failures.

Diagnostics

Use built‑in monitoring tools to quickly identify the root cause.

  • SQL Server: sys.dm_replication_monitor and Replication Monitor UI.
  • MySQL: SHOW SLAVE STATUS\G for replication health.
  • MongoDB: rs.status() and rs.printSlaveReplicationInfo().

Tips & Best Practices

  1. Keep replicas on the same network segment to reduce latency.
  2. Regularly verify that schema changes are applied consistently.
  3. Implement monitoring alerts for replication lag thresholds.
  4. Test failover scenarios in a staging environment.
  5. Document conflict resolution policies and automation scripts.

FAQ

Why is my replication lag increasing after a deployment?
Deployments often change indexes or add heavy queries. Ensure the new workload is balanced and consider scaling read replicas.
How can I reset replication after fixing a conflict?
On most platforms you can restart the replication agent or run a resync command. For SQL Server, use sp_reinitialize_replication.
What monitoring tools integrate with Azure Monitor?
Azure Database for PostgreSQL, MySQL, and SQL provide built‑in metrics. Use Azure Monitor workbooks for visualizing replication health.

Resources