Active Roles 7.3.3 - Replication: Best Practices and Troubleshooting

Replication group management

Replication group management

The tasks performed when managing a replication group include the Publisher-related tasks, such as Promote or Demote, and the Subscriber-related tasks, such as Add or Delete.

Promote

This task assigns the Publisher role to the Administration Service database server, thereby creating a replication group. When performing the Promote task, SQL Server creates the AelitaReplica publication, and starts the Snapshot Agent. The Agent creates an initial snapshot of schema and data, and saves it to the snapshot folder.

Active Roles automatically specifies and passes to SQL Server all replication settings, such as filters, type of replication, and retention period for subscriptions. For details, see Viewing replication settings later in this document.

Add

This task adds the Administration Service database server to the replication group, thus assigning the Subscriber role to the database server. When performing the Add task, SQL Server starts the Merge Agent. The Agent copies data from the Publisher’s snapshot folder to the Subscriber SQL Server. This process is referred to as applying the initial snapshot (see "Create and Apply the Snapshot" in SQL Server Books Online at http://msdn.microsoft.com/en-us/library/ms151785.aspx).

Delete

This task removes the Subscriber from the replication group, causing the database server to revert to the standalone state. When performing the Delete task, SQL Server deletes the subscription at the Publisher. The database of the former Subscriber retains the replicated data.

Demote

This task removes the Publisher from the replication group, causing the database server to revert to the standalone state. The Publisher can only be demoted after all of its Subscribers are deleted. When performing the Demote task, SQL Server deletes the AelitaReplica publication, and erases data in the snapshot folder.

Data synchronization and conflict resolution

Data synchronization and conflict resolution

After applying the initial snapshot to Subscribers, SQL Server tracks changes to published data at the Publisher and at the Subscribers:

  • When data is modified at a Subscriber, the data changes are sent to the Publisher. Then, the Publisher propagates the data changes to the other Subscribers.
  • When data is modified at the Publisher, the data changes are propagated to the Subscribers.

These operations are performed by the Merge Agents running on the Publisher SQL Server.

The Merge Agents are configured so that once data changes are made at a given replication partner, it normally takes two minutes or less for SQL Server to start synchronizing the data changes with other replication partners. The time required for the synchronization process to be completed depends on SQL Server load and on the bandwidth of network connections. As there is normally a moderate volume of data changes, the replication traffic is manageable.

The synchronization process tracks data changes on both the Subscribers and the Publisher. At the Publisher, the changes are merged to form a single version of the data. During the merge, some conflicts may be found where multiple Subscribers modified the same data.

.Any conflict between the arrived values is automatically resolved based on the Microsoft SQL Server DATETIME (Later Wins) Conflict Resolver: The winner of the conflict is chosen according to a “later wins” solution, with the last to modify the data winning the conflict. For information about conflict resolvers, see Microsoft COM-Based Resolvers in SQL Server Books Online at http://msdn.microsoft.com/en-us/library/ms152573.aspx.

SQL Server-related permissions

SQL Server-related permissions

The health of Active Roles replication heavily depends on the access permissions that the Administration Service and SQL Server Agent has on SQL Server. The required permissions are listed in the “SQL Server permissions” section in the Active Roles Quick Start Guide.

Best practices

Best practices

This section provides instructions on how to monitor replication and perform administrative tasks to resolve replication-related problems. The following topics are covered:

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