Question: Why do
we need master node in Oracle RAC ? What are the
architectural difference between the master node and the
other nodes in RAC?
able to keep track of the resources in a RAC cluster. There
is no true concept of a master node in Oracle RAC. Instead,
each instance in the cluster becomes the resource master for
a subset of resources. See
these notes on RAC.
Instead, the RAC master node has the
smallest node ID in the RAC cluster, and is usually the
first node started in the cluster. . Node-ids are
assigned to the nodes in the same order as the nodes join
the cluster. Hence, normally the node which joins the
cluster first is the master node. However, in cases
In case of
node eviction, the RAC cluster is divided into two
sub-clusters, each with it's own master node.
The sub-cluster containing fewer no. of nodes is evicted.
But, in case both the sub-clusters have same no. of nodes,
the sub-cluster having the master node survives whereas the
other sub-cluster is evicted.
You can run these OS queries to see the RAC master node:
$ORA_CRS_HOME/log/`hostname`/cssd/ocssd* |grep master
x in `ls -tr $ORA_CRS_HOME/log/`hostname`/cssd/ocssd* `; do
grep -i "master node" $x ; done | tail -1
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