Database Group Replication HA Behavior in a Two Member Cluster
Operation | Description |
---|---|
Server startup | When an
Oracle Communications Session Delivery Manager server is started it joins the cluster as a replica and election is held if there is currently no master. If the member ends up as a replica, then it is synchronized with the master during the initialization phase of the database service startup.
With the introduction of
Oracle Communications Session Delivery Manager, Release 8.0, use the following steps to start an
SDM server cluster:
|
Master member failure | When the master fails the remaining replica becomes the new master. |
Transactions (Quorum) | Transactions return successfully if a majority of the members in the cluster have replied that they received the replicated datasets. If quorum in replies from replicas is not achieved in a specific time period, the transaction fails. |
Network partition | When the master fails the remaining replica becomes the new master. |
Elections | An election can be won with a single vote. This allows the replica to be elected master in the case the master fails. |
Recovery after a network partition | In a two node cluster it is possible for the network connection between the master and replica to be partitioned or become unresponsive due to network latency. In this situation an election is held and both nodes are elected and act as masters. While in this state, write transactions can occur at both sites. As a result, special handling is required after the partition is resolved and the system recovers from a two master configuration to a single master configuration:
|
Rejoining a cluster after graceful shutdown | An election can be won with a single vote. This allows the replica to be elected master in the case the master fails. |
Rejoining cluster after shutdown for extended period | Perform a hot backup on the host running the master database before restarting a server that has been down for a long time. This avoids the potentially high cost synchronizing the server with the master during startup. |