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Chapter 23. WELCOME TO THE WORLD OF DATA... > DEALING WITH REPLICATION CONFLICTS

DEALING WITH REPLICATION CONFLICTS

Replicated databases introduce a new problem: What happens when users at different replicas simultaneously make incompatible modifications to the data or design? In Access 2000, the events that cause synchronization conflicts and errors are both viewed simply as synchronization conflicts. A single mechanism is used to record and resolve them, making resolution of such problems easier. When a conflict occurs, a resolution algorithm determines a winner and a loser. This release of replication introduces an algorithm whereby replicas in a replica set are assigned priorities, and the highest priority replica wins in a synchronization conflict. Where priorities are equal, the replica with the lowest replica ID wins. The winning record is placed in the table in both replicas. The losing record is placed in a “conflict table” and replicated to both replicas. The conflict table is a replicated table named TableName_Conflict (where TableName is the name of the table where the conflict occurred). Access automatically invokes an application, the Microsoft Replication Conflict Viewer, to help you resolve entries in conflict tables.

Understanding Data Conflicts

Consider the simple case of two users simultaneously updating the same record (row) in a RowLevelTracked table, or the same cell (column) in the record in a ColumnLevelTracked table, in different replicas. (Of course, in a traditional, non-replicated database, the locking mechanism will prevent such a problem.) When the replicas try to synchronize, Access recognizes that there's a conflict. The “winner” is the record in the replica with the higher priority.


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