Detecting and Resolving Conflicts in Logical Records

This topic covers the various combinations of conflict detection and conflict resolution approaches possible when using logical records. A conflict in merge replication occurs when more than one node changes the same data, or merge replication encounters certain types of errors, such as a constraint violation, when replicating changes. For more information about conflict detection and resolution, see Advanced Merge Replication Conflict Detection and Resolution.

To specify the conflict tracking and resolution level for an article

• Microsoft SQL Server Management Studio: How to: Specify the Conflict Tracking and Resolution Level for Merge Articles (SQL Server Management Studio)
• Replication Transact-SQL programming: How to: Specify the Conflict Tracking and Resolution Level for Merge Articles (Replication Transact-SQL Programming)

Conflict Detection

The way in which conflicts are detected for logical records is determined by two article properties: column_tracking and logical_record_level_conflict_detection. Previous versions of SQL Server supported row- and column-level conflict detection; SQL Server 2005 also supports logical record-level detection. For more information on row-level and column-level tracking see the "Tracking Level" section of How Merge Replication Detects and Resolves Conflicts.

The logical_record_level_conflict_detection article property can be set to TRUE or FALSE. The value should only be set for the top-level parent article and will be ignored by child articles. If this value is FALSE, merge replication detects conflicts as in previous versions of SQL Server, based solely on the value of the column_tracking property for the article. If this value is TRUE, merge replication will ignore the column_tracking property of the article, and detect a conflict if changes are made anywhere in the logical record. For example, consider this scenario:

A conflict is detected if two users change any values for the Customer2 logical record in the Customers, Orders, or OrderItems tables. This example involves changes made via an UPDATE statement, but the conflict can also be detected by changes made with INSERT or DELETE statements.

Conflict Resolution

By default, merge replication uses priority-based logic to resolve conflicts. If a conflicting change is made in two Subscriber databases, the change for the Subscriber with the higher subscription priority wins, or if the priority is the same, the first change to reach the Publisher wins. With row-level and column-level detection, the entire winning row always overwrites the losing row.

The logical_record_level_conflict_resolution article property can be set to TRUE or FALSE. The value should only be set for the top-level parent article and will be ignored by child articles. If the value is TRUE, the entire winning logical record overwrites the losing logical record. If it is FALSE, individual winning rows can come from different Subscribers or Publishers. For example, Subscriber A could win a conflict on a row from the Orders table, and Subscriber B could win on a related row from the OrderItems table. The result is a logical record with the Orders row from Subscriber A and the OrderItems row from Subscriber B.

Interaction of Conflict Resolution and Detection Settings

The outcome of conflicts depends on the interaction of conflict detection and resolution settings. For the examples below, it is assumed that the priority-based conflict resolution is being used. When using logical records, the possibilities are:

• Row or column level detection, row level resolution
• Column level detection, logical record resolution
• Row level detection, logical record resolution
• Logical record detection, logical record resolution

Row or Column Level Detection, Row Level Resolution

In this example, the publication is configured with:

• column_tracking is TRUE or FALSE
• logical_record_level_conflict_detection is FALSE
• logical_record_level_conflict_resolution is FALSE

In this case, detection is at the row or column level and resolution is at the row level. These settings are used to take advantage of having all changes to a logical record replicate as a unit, but without conflict detection or resolution at the logical record level.

Column Level Detection, Logical Record Resolution

In this example, the publication is configured with:

• column_tracking is TRUE
• logical_record_level_conflict_detection is FALSE
• logical_record_level_conflict_resolution is TRUE

A Publisher and Subscriber start with the same data set, and a logical record is defined between the orders and customers tables. The Publisher changes the custcol1 column in the customers table and the ordercol1 in the orders table. The Subscriber changes custcol1 in the same row of the customers table and the ordercol2 column in the same row of the orders table. The changes to the same column in the customer table result in a conflict, but the changes to the orders table are not in conflict.

Because the conflicts are resolved at the logical record level, the winning changes made at the Publisher replace the changes made in the Subscriber tables during replication processing.

Row Level Detection, Logical Record Resolution

In this example, the publication is configured with:

• column_tracking is FALSE
• logical_record_level_conflict_detection is FALSE
• logical_record_level_conflict_resolution is TRUE

A Publisher and Subscriber start with the same data set. The Publisher changes the custcol1 column in the customers table. The Subscriber changes custcol2 in the customers table and the ordercol2 column in the orders table. The changes to the same row in the customers table result in a conflict, but the Subscriber changes to the orders table are not in conflict.

Because the conflicts are resolved at the logical record level, during synchronization the winning changes made at the Publisher replace the changes made in the Subscriber tables.

Logical Record Detection, Logical Record Resolution

In this example, the publication is configured with:

• logical_record_level_conflict_detection is TRUE
• logical_record_level_conflict_resolution is TRUE

A Publisher and Subscriber start with the same data set. The Publisher changes the custcol1 column in the customers table. The Subscriber changes the ordercol1 column in the orders table. There are no changes to the same row or columns, but because the changes are made in the same logical record for custid=1, the changes are detected as a conflict at the logical record level.

Because the conflicts are also resolved at the logical record level, during synchronization the winning change made at the Publisher replaces the change made in the Subscriber tables.

See Also

Concepts

Grouping Changes to Related Rows with Logical Records

Help and Information

Getting SQL Server 2005 Assistance