After a conflict is detected, the Merge Agent launches the selected conflict resolver and uses the resolver to determine the conflict winner. The winning row is applied at the Publisher and Subscriber, and the data from the losing row is written to a conflict table. Conflicts are resolved immediately after the resolver executes, unless you select to resolve conflicts interactively.
Resolver Types
In merge replication, conflict resolution takes place at the article level. For publications composed of several articles, you can have different conflict resolvers serving different articles, or the same conflict resolver serving one article, several articles, or all the articles comprising a publication.
If you plan to use the default priority-based conflict resolver, you do not have to set the resolver property of an article. If you want to use an article resolver instead of the default resolver, you must set the resolver property for the article that will use it by selecting an available resolver on the Publisher. Any specific information that needs to be passed to the resolver can also be specified in the resolver information property.
Merge replication offers four types of conflict resolvers:
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The default priority-based conflict resolver
The default resolution mechanism behaves differently, depending on whether a subscription is a client subscription or a server subscription. You assign priority values to individual Subscribers that use server subscriptions; changes made at the node with the highest priority win any conflicts. For client subscriptions, the first change written to the Publisher wins the conflict. For more information about subscription types, see the section "Subscription Types" in How Merge Replication Detects and Resolves Conflicts.
After a subscription is created, it cannot be changed from one type to another.
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A business logic handler
The business logic handler framework allows you to write a managed code assembly that is called during the merge synchronization process. The assembly includes business logic that can respond to conflicts and a number of other conditions during synchronization. For more information, see Executing Business Logic During Merge Synchronization.
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A COM-based custom resolver
Merge replication provides an API for writing resolvers as COM objects in languages such as Microsoft Visual C++ or Microsoft Visual Basic. For more information, see COM-Based Custom Resolvers.
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A COM-based resolver supplied by Microsoft
Microsoft SQL Server includes a number of COM-based resolvers. For more information, see Microsoft COM-Based Resolvers.
For information about how to select the appropriate type of resolver, see Choosing a Resolver.
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Some article resolvers are written to handle conflicts only for certain operations. For example a resolver might handle updates, but not inserts or deletes. The default priority-based conflict resolver handles any conflicts not handled by the article resolver.
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To specify a merge subscription type and conflict resolution priority
Interactive Resolver
Replication supplies an Interactive Resolver user interface that can be used in conjunction with either the default priority-based conflict resolver or an article resolver. When performing on-demand synchronization through Microsoft Windows Synchronization Manager, the Interactive Resolver displays conflict data at run-time, and lets you choose how to resolve conflicts. For more information about how to enable interactive resolution and launch the Interactive Resolver, see Interactive Conflict Resolution.