Persistence Servers and Clusters
A persistence server is a process that implements one or more persistence stores. Several servers can cooperate in a persistence cluster.
The servers within the cluster communicate among themselves to replicate message data and acknowledgment data. Replication ensures that the cluster can continue to deliver messages to subscribers, even when some of the servers are unavailable.
Administrators define clusters and their servers within the realm. You can define any number of clusters in the realm. A cluster consists of a set of persistence servers.
A cluster as a whole maintains a set of persistence stores, replicating their data among its servers for fault tolerance.
To ensure the benefits of in-memory replication and fault-tolerant service, each server of a cluster must run on a dedicated host computer.
- Quorum and Leader
A persistence cluster can interact with clients only when a quorum of servers exists. This requirement ensures correct replication and fault tolerance. - Quorum Conditions General Rule
A valid quorum ensures correct replication and fault tolerance. As a general rule, a group of candidate servers must satisfy all three of the following conditions to form a valid quorum. - Cluster Size
For delivery assurance with fault tolerance, use a minimum cluster size of 3 servers, so that a quorum can exist even when one server is unavailable. - Quorum Behaviors
The persistence servers in a cluster exhibit these behaviors as they form and maintain a quorum. - Persistence Server Fault Tolerance
Replication of data among a quorum of servers ensures that the cluster as whole remains complete and correct, despite temporary outage of some of its servers.