Reason for Node eviction in Oracle RAC Environment

In Oracle Real Application Clusters (RAC), the eviction of a node from the cluster is typically a result of the Oracle Clusterware’s attempt to maintain the integrity and stability of the cluster in the face of various issues such as communication failures, network partitions, or hardware problems. The eviction process is designed to prevent split-brain scenarios and ensure that the remaining nodes in the cluster can operate cohesively.

Here are some common scenarios in which a node may be evicted from an Oracle RAC cluster:

Loss of Communication:

If a node loses communication with the other nodes in the cluster, and the remaining nodes cannot reach a consensus on the status of the isolated node, the Oracle Clusterware may initiate the eviction of the isolated node. This helps avoid split-brain scenarios where nodes operate independently without coordination.

Voting Disk Inaccessibility:

The Oracle Clusterware uses a Voting Disk to determine the membership and health of the cluster. If a node loses access to the Voting Disk, it may be evicted to prevent it from making independent decisions that could lead to inconsistencies in the cluster.

Network Partition:

In the case of a network partition where nodes are separated into isolated groups, the Oracle Clusterware may decide to evict nodes in one of the partitions to maintain a cohesive cluster with a majority of votes.

Manual Intervention:

Administrators can manually initiate the eviction of a node, for example, during planned maintenance activities or if they determine that a node is causing issues in the cluster. Manual eviction is typically done through Oracle Clusterware utilities or commands.

Split Brain Resolution:

The eviction process is often part of a split-brain resolution mechanism. If the Oracle Clusterware detects a split-brain scenario, where nodes have lost communication but continue to operate independently, it may evict nodes to resolve the inconsistency.
The specific conditions and triggers for node eviction may vary based on the Oracle Clusterware version and configuration. Oracle Clusterware employs a voting mechanism, where a majority of nodes must agree on the cluster membership status to avoid split-brain situations. The voting mechanism ensures that a clear decision-maker exists in the event of network issues or node failures.