Merge Replication Conflicts

A merge replication conflict in SQL Server occurs when the same data is modified concurrently at different nodes (publisher, subscriber, or both) in a merge replication topology, leading to inconsistencies when changes are synchronized. Merge replication allows multiple nodes to independently update data, and during synchronization, the Merge Agent reconciles these changes. Conflicts arise under scenarios like:

• Update Conflict: The same row is updated at different nodes with different values.
• Insert Conflict: Rows with the same primary key are inserted at different nodes.
• Delete/Update Conflict: One node deletes a row while another updates it.

Key Aspects of Merge Replication Conflicts:

• Detection: SQL Server tracks changes using metadata (e.g., row GUIDs, lineage columns) to identify conflicts during synchronization.
• Resolution: Conflicts are resolved based on predefined rules, such as:
  • Default Resolver: The publisher’s changes typically take precedence (configurable).
  • Custom Resolver: User-defined logic or stored procedures to handle conflicts.
  • Interactive Resolver: Manual resolution via tools like SQL Server Management Studio.
• Conflict Tracking: Conflicts are logged in conflict tables (e.g., MSmerge_conflicts_info) for review and auditing.

For example, if a row in a replicated table is updated to “Value A” at the publisher and “Value B” at the subscriber, the Merge Agent detects the conflict and applies the resolver’s logic to determine which value persists.

To minimize Merge Replication Conflicts:

Design applications to avoid concurrent updates to the same data, partition data logically, or use conflict resolvers tailored to business needs. For detailed monitoring, use SQL Server’s conflict viewer or query conflict tables.

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