What does node eviction mean in the Oracle RAC world?

Question

Software environment: Oracle 12c with RAC running on RHEL

The question might sound rather banal, but I wasn't able to find any word on this in the Oracle documentation I read thus far.

By searching the net, I came to the conclusion that node evictions usually imply a node reboot, but that doesn't always seem to be the case, some suggest node evictions without node reboots are also possible. If that is indeed the case, when will the node be rebooted and when not? If a node cannot access the minimum required number of voting disks, then that node will be evicted. Will that node always be rebooted because of this eviction? Can one configure this behavior (i.e. change from eviction with reboot to eviction without reboot)?

Answer 1

What is node eviction?

Word Meaning(Merriam Webster Disctionary): to force(someone) to leave the place.

The process of removing the failed(due to various reasons) node from the cluster is known as eviction. Prior to 11gR2 Oracle tries to prevent from split brain situation by quickly rebooting the failed node . After 11gr2 Clusterware will attempt to clean up the failed resources . If the clusterware is able to clean up the failed resources, OHASD will try to restart the CRS stack. Once this task is done all the cluster resources on that node will be started automatically. This is called reboot less fencing(or eviction). If clusterware can not stop or clean the failed resources then it will roboot the node.

Causes of node eviction

-Missing network heartbeat
-Missing disk heartbeat
-CPU starvation issues
-Hanging cluster processes
-May have more...

Will that node always be rebooted?

Same applies as above mentioned.

Can one configure this behavior?

No, Oracle Clusterware will decide on it.

If you want to learn more on it you can google the term 'Rebootless Node Fencing or Eviction' I promise you will have number of options to carry on.