Hierarchical Replication Topologies

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Hierarchical Replication Topologies

Enterprise Replication provides two types of Hierarchical Routing topology:

HR Topology Terminology

Enterprise Replication uses the terms in the Table 13 to describe Hierarchical Routing topology.

Table 13. Replication Topology Terms
Term	Definition
Root server	An Enterprise Replication server that is the uppermost level in a hierarchically organized set of information The root is the point from which database servers branch into a logical sequence. All root database servers within Enterprise Replication must be fully interconnected.
Nonroot server	An Enterprise Replication server that is not a root database server but has a complete global catalog and is connected to its parent and to its children
Tree	A data structure that contains database servers that are linked in a hierarchical manner The topmost node is called the root. The root can have zero or more child database servers; the root is the parent database server to its children.
Parent-child	A relationship between database servers in a tree data structure in which the parent is one step closer to the root than the child.
Leaf server	A database server that has a limited catalog and no children.

A root server is fully connected to all other root servers. It has information about all other replication servers in its replication environment. Figure 10 shows an environment with four root servers.

A nonroot server is similar to a root server except that it forwards all replicated messages for other root servers (and their children) through its parent. All nonroot servers are known to all root and other nonroot servers. A nonroot server might or might not have children. All root and nonroot servers are aware of all other servers in the replication environment.

Important:

In Hierarchical Routing topologies, Enterprise Replication specifies the synchronization server as the new server's parent in the current topology. For more information, see Customizing the Replication Server Definition and cdr define server.

Hierarchical Tree

A hierarchical tree consists of a root database server and one or more database servers organized into a tree topology. The tree contains only one root, which has no parent. Each database server within the tree references its parent. A database server that is not a parent is a leaf. Figure 11 illustrates a replication tree.

Figure 11. Hierarchical Tree Topology

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In Figure 11, the parent-child relationship within the tree is as follows:

Asia is the parent of China and Japan.
China is the child of Asia and the parent of Beijing, Shanghai, and Guangzhou.
Guangzhou is the child of China and the parent of Hong Kong.

Asia is the root database server. Japan, China, and Guangzhou are nonroot database servers. You can define Beijing, Shanghai, and Hong Kong as either nonroot database servers or leaf database servers, depending on how you plan to use them. The dashed connection from China to Shanghai indicates that Shanghai is a leaf server.

Parent servers are good candidates for using HDR to provide backup servers. For more information, see Hierarchical Replication Topologies.

Forest of Trees

A forest of trees consists of several hierarchical trees whose root database servers are fully connected. Each hierarchical tree starts with a root database server. The root database servers transfer replication messages to the other root servers for delivery to its child database servers. Figure 12 shows a forest of trees.

Figure 12. Forest-of-Trees Topology

In Figure 12, North America, Asia, and Europe are root database servers. That is, they are fully connected with each other. France and Germany are in a tree whose root is Europe. Asia is the root for the six database servers in its tree.

In a forest of trees, all replication messages from one tree to another must pass through their roots. For example, a replication message from Beijing to France must pass through China, Asia, and Europe.

Organizing the database servers in a hierarchical tree or a forest of trees greatly reduces the number of physical connections that are required to make a replication system. If all the database servers in Figure 12 were fully connected, instead of being organized in trees, 55 connections would be required.

To ensure that all servers retain access to the replication system, use HDR on parent servers. For more information, see Using HDR in a Forest of Trees Topology.