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The Replication Manager is an important component of the Fault Tolerance Infrastructure that interacts with other components
of the infrastructure. Typically, the Replication Manager is replicated for fault tolerance, though not necessarily on every
host within the fault tolerance domain; however, logically, there is a single Replication Manager for each fault tolerance
domain.
The Replication Manager inherits three application program interfaces: PropertyManager, GenericFactory, and ObjectGroupManager.
The PropertyManager interface allows properties of the object groups to be set, such as the ReplicationStyle, MembershipStyle,
ConsistencyStyle, InitialNumberReplicas, MinimumNumberReplicas, etc. These properties may be set statically as defaults for
the fault tolerance domain or for a particular type, or may be set or changed dynamically while the application is executing.
The GenericFactory interface is used by the application to create object groups, as
shown in Figure 23-4 on page 23-32. It is also used by the Replication Manager to
create individual members of an object group.
For the infrastructure-controlled Membership Style, the Replication Manager invokes the individual factories, for the appropriate
locations, to create the members of the object group, both initially to satisfy the InitialNumberReplicas property, and after
the loss of a member because of a fault to satisfy the MinimumNumberReplicas property. The Replication Manager adds the members
to the object group and creates the object group reference. Subsequently, the Replication Manager removes members, if necessary.
For the application-controlled Membership Style, the ObjectGroupManager interface allows the application to create a member
of an object group, to add an existing object to an object group, or to remove a member from an object group, citing the location
of the member to be created, added, or removed. It also allows the application to define the primary member of an object group
and to query the locations of the members of an object group and the primary member.
set
roperties create_ Invoked by the Application for object() Infrastructure-Controlled and Replication Manager Application-Controlled
Membership Styles
Object
Property
Group create_ Invoked by the Application for
Manager
Manager member() Application-Controlled Membership Style
add_
Generic Factory member()
create_ object() |
Invoked by Replication Manager on |
Host H2 |
Host H3 |
||
| Factory Objects | |||||
| Object Replica | Object Replica | ||||
| S1 |
 |
S2 |
 |
||
| Factory | Factory | ||||
| ORB | ORB |
Figure 23-4 The Replication Manager and the Creation of an Object Group