在 RAC 集群中，当发生脑裂时，应当驱除哪些节点？又是如何判断的呢？

在 Oracle 11.2 及以前，当集群脑裂，总是节点号最小的节点会幸存，这一行为，在 12.1.0.2 版本中，被新特性替代。新特性启用了节点权重计算法，当发生 split brain 时，会驱逐权重低的节点，权重高节点幸存，以减少对于业务系统的影响。

In 11.2 or even older version, the lowest number node will survive when split brain takes place, however this has changed in 12.1.0.2 with the introduction of node weight. Started from 12.1.0.2, during split brain resolution, node with higher weight will survive:

以下是来自文档中的示范：

2014-11-24 14:25:41.140603 : CSSD:1117321536: clssnmrCheckNodeWeight: node(1) has weight stamp(0), pebble(0)
2014-11-24 14:25:41.140609 : CSSD:1117321536: clssnmrCheckNodeWeight: node(2) has weight stamp(311972654), pebble(3)
2014-11-24 14:25:41.140612 : CSSD:1117321536: clssnmrCheckNodeWeight: stamp(311972654), completed(1/2)
2014-11-24 14:25:41.140615 : CSSD:1117321536: clssnmrCheckSplit: Waiting for node weights, stamp(311972654)
2014-11-24 14:25:41.188880 : CSSD:1084811584: clssnmvDiskKillCheck: not evicted, file /dev/raw/raw2 flags 0x00000000, kill block unique 0, my unique 1416805718
2014-11-24 14:25:41.558921 : CSSD:1114167616: clssnmvDiskPing: Writing with status 0x3, timestamp 1416810341/1022717334
2014-11-24 14:25:41.731912 : CSSD:1086388544: clssnmvDHBValidateNCopy: node 1, node1, has a disk HB, but no network HB, DHB has rcfg 311972655, wrtcnt, 9527468, LATS 102 2717514, lastSeqNo 9527467, uniqueness 1416808381, timestamp 1416810341/1022722074
2014-11-24 14:25:41.731928 : CSSD:1086388544: clssnmvReadDskHeartbeat: manual shutdown of nodename node1, nodenum 1 epoch 1416810341 msec 1022722074
2014-11-24 14:25:41.732266 : CSSD:1117321536: clssnmrCheckNodeWeight: node(2) has weight stamp(311972654), pebble(3)
2014-11-24 14:25:41.732273 : CSSD:1117321536: clssnmrCheckNodeWeight: stamp(311972654), completed(1/1)
2014-11-24 14:25:41.732294 : CSSD:1117321536: clssnmCheckDskInfo: My cohort: 2
2014-11-24 14:25:41.732299 : CSSD:1117321536: clssnmRemove: Start
2014-11-24 14:25:41.732306 : CSSD:1117321536: (:CSSNM00007:)clssnmrRemoveNode: Evicting node 1, node1, from the cluster in incarnation 311972655, node birth incarnation 311972654, death incarnation 311972655, stateflags 0x225000 uniqueness value 1416808381 The number of the resource executing on each node and others are considered by the weight.

clssnmrCheckNodeWeight 用于来检查权重，以上日志显示，node(2) has weight stamp(311972654) 节点二具备更高权重，将会幸存下来。而节点一被驱逐。

参考文档：12c: Which Node Will Survive when Split Brain Takes Place (Doc ID 1951726.1)