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RE: Oracle CRS and Split Brin

From: Kevin Closson <>
Date: Wed, 28 Mar 2007 09:25:47 -0700
Message-ID: <>


When the master node looses its private network, the surviving node becomes the master, reconfiguration of the cluster takes place - the old master is ejected from the cluster configuration - and rebooted. The following can be seen in its crsd.log file (this is for the crs component of the oracle clusterware, responsible for managing oracle resources):

I AM THE NEW OCR MASTER at incar 6. Node Number = 1

..[...lots good CRS stuff deleted...]

...This was a very good follow up, but the question was about split
brain. Split brain is when there is an equal number of "survivors" and both "think" they are the sole survivor. I think the original post was asking how Oracle determines who gets to anoint themselves the new master in a split brain scenario. I have not seen the full algorithm Oracle uses documented anywhere on the net so if someone has, please let us know. There are a lot of cluster implementations out there. One common approach is to maintain knowledge of the IP addresses of members and use the lowest IP node as one of the factors in choosing the winner in a SB scenario. That is not how CRS does it though as has become evident in a thread I've had with a reader of my blog. In his 2 node case his CRS master was also the lowest IP and in a meltdown scenario, the other node was chosen as the sole survivor. That really surprised me.

I think all I've said is Oracle is not telling us what the full algorithm is for survivorship in a true split-brain scenario.

There are some clusterware topics here: lusters-related-topics/

Such as inux-rac-fencing-also-fencing-failures-split-brain/    

Received on Wed Mar 28 2007 - 11:25:47 CDT

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