Directory Replication Groups

This section contains these topics:

• Data Transfer Between Nodes in a Directory Replication Group

• Single-Master Replication Groups

• Multimaster Replication Groups

• Fan-Out Replication Groups

• Types of Directory Replication Compared

• Multimaster Replication with Fan-Out

  See Also: "Replication Agreements"

Data Transfer Between Nodes in a Directory Replication Group

In a directory replication group, the protocol for transferring data can be based on either Oracle9i Advanced Replication or LDAP. Table 24-2 shows how each type handles various features of replication and points to sections of this chapter with more details.

Table 24-2  Types of Data Transfer Between Nodes in a Directory Replication Group

Feature	LDAP-Based Replication	Oracle9i Advanced Replication-Based Replication	More Information
Change propagation	Change propagation from supplier to consumer happens over LDAP	Change propagation from supplier to consumer happens by using Oracle9i Advanced Replication	"Change Logs in Directory Replication"
Replica type supported	Read-only full replica Read-only partial replica	Read/write full replica	"Full Directory Replication" "Partial Directory Replication"
Configuration supported	Single-master replication Fan-out replication	Multimaster replication Single-master replication, by switching all masters in a multimaster configuration except one to read-only mode.	"Single-Master Replication Groups" "Multimaster Replication Groups" "Fan-Out Replication Groups"

Single-Master Replication Groups

A single-master replication group has only one supplier replica supplying changes to one or more consumers. Clients can update only the master replica, and can only read data on any of the consumers.

Figure 24-2 shows a single-master replication environment.

Figure 24-2 Example of Single-Master Replication

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In Figure 24-2, each bullet represents a node of Oracle Internet Directory. Node A is a supplier that replicates consumer nodes B and C. Node A is read/write, and Nodes B and C are read-only. The data transfer protocol is LDAP.

Multimaster Replication Groups

A multimaster replication group, also called a peer-to-peer or n-way replication group, has two or more nodes acting as equals to manage groups of replicated data. In a multimaster replication group, each directory server is both a supplier and a consumer of changes, and the entire directory is replicated on each node.

The example in Figure 24-3 shows three nodes--A, B, and C--that update each other in a multimaster replication group.

Figure 24-3 Example of Multimaster Replication

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In Figure 24-3, each node is read/write, and the data transfer protocol is based on Oracle9i Advanced Replication.

Note: Multimaster replication is the only replication mechanism supported in Oracle Application Server Single Sign-On as described in the section "Configuring Oracle Application Server Single Sign-On for Replication" in the chapter on high availability in the Oracle Application Server Single Sign-On Administrator's Guide

See Also: "Multimaster Replication" for more information about multimaster replication

Fan-Out Replication Groups

A fan-out replication group, also called a point-to-point replication group, has a supplier replicating directly to a consumer. That consumer can then supply the same data to one or more other consumers. The replication can be either full or partial.

Figure 24-4 shows a fan-out replication environment.

Figure 24-4 Example of Fan-Out Replication

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In Figure 24-4, supplier A replicates to two consumers, B and C. Consumer node B contains a partial replica of A, whereas consumer node C contains a full replica of A. Both consumer nodes B and C are read-only.

Each of these nodes, in turn, serves as a supplier that replicates data to two other consumers: Node B partially replicates to nodes D and E, and node C fully replicates to nodes F and G.

In fan-out replication, nodes transfer data by using LDAP.

Types of Directory Replication Compared

Table 24-3 compares multimaster, single-master, and fan-out replication.

Table 24-3  Multimaster. Single-Master, and Fan-Out Replication Compared

Multimaster Replication	Single-Master Replication	Fan-out Replication
Uses only Oracle9i Advanced Replication	Uses LDAP-based replication	Uses LDAP-based replication
Updates can be made on any node, whether supplier or consumer.	Updates can be made on the supplier only. Changes to a consumer can be propagated to other fan-out consumers, but not back to the supplier.	Updates can be made on the supplier only. Changes to a consumer can be propagated to other fan-out consumers, but not back to the supplier. This is also true when the LDAP-based replica node is read/write.

Multimaster Replication with Fan-Out

Oracle Internet Directory Release 9.0.4 enables any node in a multimaster replication group to supply all or part of its data to a read-only consumer. This consumer can, in turn, supply data to other consumers in a fan-out configuration. Within the multimaster replication agreement, data transfer between the nodes occurs by way of Oracle9i Advanced Replication. Within the fan-out replication agreement, data transfer from supplier to consumer occurs by way of LDAP.

Note: If an LDAP-based replica is read/write, then changes on this node propagate to consumers, but not to suppliers.

Figure 24-5 shows an example of multimaster replication used in conjunction with fan-out replication.

Figure 24-5 Example of Multimaster Replication with Fan-Out

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In the example in Figure 24-5, nodes A, B, and C form a multimaster replication group. They transfer data between them by using Oracle9i Advanced Replication.

Node B supplies changes to Node D, a read-only replica of the entire directory. Node D, in turn, supplies changes to Nodes F and G by using LDAP-based replication. Both Nodes F and G are read-only replicas of the entire directory. Similarly, Node C supplies changes to node E, a read/write replica of the entire directory. Node E, in turn supplies changes to Node H, a read-only replica of the entire directory, and Node I, a read-only partial replica, by using LDAP-based replication.

See Also: "Fan-Out and Partial Replication" for more information about fan-out replication