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Don Burleson Blog 







RAC node eviction tips

Oracle Database Tips by Donald BurlesonAugust 27, 2015

 I understand what can cause a RAC node to be evicted from the cluster, but I can't find the process for deciding which node will be rebooted after the eviction. Oracle's explanations on MOSC say "a node" but in my testing it is always a particular physical machine and not the secondary instance.

What would happen in a 3 or 4 node cluster when you have a RAC node eviction? Is it safe to assume it will be instance 2 every time no matter which side of the interconnect goes down? Also what are some of the most common reasons for a node eviction?
Answer: A RAC node eviction is done on this basis. When a condition that requires a node eviction occurs (see below) The node with the lowest node number will be the node the "survives" the eviction. When you have a three node cluster, two nodes will survive a node eviction, and so on.

A node eviction is done when a heartbeat indicates that a node is not responding, and the evicted node is re-started so that it can continue to partiipate in the cluster.


Reason for RAC node evictions

There are many reasons for a RAC node eviction. Oracle's Cluster Health Monitor, (formerly known as the Instantaneous Problem Detector for Clusters (IPD/OS)), automatically collects OS performance metrics on a regular basis to assist with diagnosing node evictions.


- Hardeware Failure: A failure of any of the major hardware components (CPU, RAM, network interconnect) can cause a node eviction.

- Server Overload: A server that is expericncing RAM swapping might trigger a node eviction. It's important that each node be properly configured.

- Voting disk communications This can happen when communications to the voting disk is interrupted, causing the disconnected node to be evicted and re-boot.

- Database issues If the database (or the ASM instance) is not responding (a database "hang" condition), then a node eviction may occur.



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