Node eviction in Oracle Real Application Clusters (RAC) can happen for a variety of reasons. Some of the most common reasons for node eviction include:
- Network failure: If the network connection between nodes is lost or becomes unavailable, the cluster may determine that one of the nodes is no longer accessible and evict it from the cluster.
- Instance failure: If an instance on a particular node fails, the cluster may decide to evict that node in order to prevent any further issues with the failed instance.
- Resource exhaustion: If a node runs out of a critical resource, such as memory or disk space, the cluster may evict the node in order to prevent the issue from affecting the entire cluster.
Node eviction is typically a last resort measure that is used to protect the integrity of the cluster and ensure that it continues to function properly.
What to do when node is evicted in RAC ?
When a node is evicted from an Oracle Real Application Clusters (RAC) system, the first thing you should do is investigate the reason for the eviction. There may be an issue with the network, an instance failure, or some other issue that caused the eviction to occur. Once you have identified the reason for the eviction, you can take steps to address the underlying issue and prevent future evictions from occurring.
If the eviction was caused by a network failure, for example, you may need to troubleshoot the network connectivity between the nodes or replace faulty network hardware. If the eviction was caused by an instance failure, you may need to restart the failed instance or take other corrective action.
In some cases, it may be necessary to manually re-join the evicted node to the cluster. This can be done using the crsctl add node command, which allows you to add a node back into the cluster after an eviction. Before re-joining the node, however, you should make sure that the underlying issue has been resolved and that the node is ready to re-join the cluster.
Overall, the steps for dealing with a node eviction in Oracle RAC will depend on the specific circumstances of the eviction and the underlying cause of the problem.
What happens Internally when a Node is evicted ?
When a node is evicted from an Oracle Real Application Clusters (RAC) system, several things happen internally to ensure that the cluster continues to function properly. Here are some of the key steps that take place during a node eviction:
- The cluster manager (CRS) detects that the node has been evicted and initiates a clean-up process to free up any resources that were being used by the evicted node. This may include releasing locks, freeing memory, and cleaning up other resources that were in use by the evicted node.
- The CRS sends notifications to other nodes in the cluster, informing them that the node has been evicted and providing information about the current state of the cluster. This allows the other nodes to update their view of the cluster and ensure that they are aware of the current status of all nodes.
- The CRS updates the cluster registry to reflect the new state of the cluster, removing any information about the evicted node and adding any new information about other nodes that may have joined the cluster since the eviction occurred.
- The CRS may also initiate a re-balancing process to redistribute workload across the remaining nodes in the cluster. This can help to ensure that the cluster continues to operate efficiently and effectively, even after a node has been evicted.
Overall, the process of node eviction in Oracle RAC is designed to ensure that the cluster continues to operate smoothly and efficiently, even when a node has been evicted.
When does the evicted node will be readded in RAC ?
When a node is evicted from an Oracle Real Application Clusters (RAC) system, it will typically be re-added to the cluster automatically once the underlying issue that caused the eviction has been resolved. For example, if the eviction was caused by a network failure, the evicted node will be re-added to the cluster once the network connectivity has been restored.
In some cases, however, it may be necessary to manually re-add the evicted node to the cluster. This can be done using the crsctl add node command, which allows you to add a node back into the cluster after an eviction. Before re-adding the node, you should make sure that the underlying issue has been resolved and that the node is ready to re-join the cluster.
It's important to note that the process of re-adding a node to the cluster can be complex and can have significant consequences for the overall health and performance of the cluster. As a result, it's generally recommended to only re-add a node to the cluster under the guidance of a qualified Oracle DBA or other experienced professional.
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