Merge replication is a bi-directional replication where the data changes that occur on the publisher and the subscriber are merged at the time of synchronization. In this article, we will discuss how merge replication detects conflicts and how they are resolved using the default and custom conflict handlers.
Conflict Detection
Conflicts occur whenever data changes both on the publisher and the subscriber at the time of synchronization. Merge replication allows you to specify whether you want conflicts to be recognized at a row-level or at a column-level based on your business requirements.
When row-level conflict detection is enabled, changes to a particular row in the table on the publisher and the subscriber will be considered a conflict even though the columns changed may be different. On the other hand, with column-level conflict detection, the data changes must happen to the same columns in a particular row on both the publisher and the subscriber.
Conflict Resolution
SQL Server provides a range of conflict resolvers to handle conflicts in merge replication. The default resolver is a priority-based resolver, where you can assign different priority values to the subscribers to determine who would win in the case of a conflict.
If the default resolver does not meet your business requirements, you can choose to use a custom resolver. Custom resolvers are specific to a table and can be implemented using COM-based custom resolvers, stored procedure-based custom resolvers, or one of the built-in custom resolvers provided by SQL Server.
Custom Resolvers
If you choose to use a custom resolver, you can specify it by clicking on the Table Properties button and selecting the Resolver tab. SQL Server provides a number of custom resolvers, such as the Maximum Conflict Resolver, Averaging Conflict Resolver, and Subscriber Always Wins Conflict Resolver.
If none of the built-in custom resolvers suit your needs, you can write a COM-based custom resolver using Visual Basic or VC++ and register the DLL at the server where the merge agent runs. Alternatively, you can write a stored procedure-based custom conflict resolver that uses T-SQL to implement your business logic.
Conclusion
In conclusion, merge replication in SQL Server provides various conflict detection and resolution options to meet your business requirements. Whether you choose the default resolver or a custom resolver, it is important to carefully consider the conflict detection type and the conflict resolution strategy to ensure data integrity in your replication environment.
By understanding how conflicts are detected and resolved in merge replication, you can effectively manage data changes and ensure synchronization between the publisher and the subscriber.
Thank you for reading!