Sunday, October 30, 2011

Study: Replication Models in SQL Server 2008

The replication architecture is as extensive as tricky. Therefore, it has become versatile enough to meet all the needs of almost all replicated situations. Fortunately or unfortunately, configuring the replication process is little bit tricky. If you still wish to make the replication process smooth, we should be aware of selecting a specific replication model and performing any necessary preliminary tasks before we start configuring the replication.

Selecting the physical layout of the publisher, distributor and the subscriber database is the main decision to for a replication model. The following are the some common replication models that we use.

Peer-to-peer model: This lets us replicate between identical participants in the topology. The advantage of this model is that it permits roles to move between replicated nodes dynamically for maintenance or failure management. The disadvantage is the additional administration overhead involved with moving roles.

Central subscriber model: A single subscriber database that collects data from several publishers. For example, if you have ServerA, ServerB, and ServerC, ServerA and ServerB act as central publishers and ServerC acts as the central subscriber. In this configuration, when updates are distributed from ServerA and ServerB, they are collected on ServerC. A central subscriber can then republish the combined data to other servers. To use this model, all tables used in replication must have a unique primary key; otherwise, the replication model will not work properly.
Central publisher with remote distributor model: Maintains the publisher and distributor databases on different servers, with one or more subscribers configured on other servers. The advantage of this model is that the workload is more evenly distributed. The disadvantage is that you have to maintain an additional server.
Publishing subscriber model: Relays the distribution of data to other subscribers; you can use this with any of the other models. For example, if you have two geographically separated sites, a publisher can replicate data to servers at site A and then have a publishing subscriber at site B that distributes the data to servers at site B.
The central publisher model: is the most commonly used replication model. Unfortunately, you will often find that the extra load on the publication server will slow down server performance. To reduce the server load, you should put the distributor on its own server. Be aware, however, that doing this will not entirely eliminate the workload on the publication server. The publisher and distributor still need to communicate, and they still need to pass data back and forth.
Central publisher model: Maintains the publisher and distributor databases on the same server, with one or more subscribers configured on other servers. The advantages of this model are manageability and ease of maintenance. The disadvantages include the extra workload and resource usage on the publication server.

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