Capacity Planning and Architecture - Expert Oracle RAC Performance Diagnostics and Tuning - page 31

The network layer that consists of both the IPC and transmission control protocol (TCP) in a clustered
configuration is responsible for packaging the messages and passing them to and from the communication layer for
the interconnect access.
Various monitoring processes consistently verify different areas of the system. The heartbeat monitor continually
verifies the functioning of the heartbeat mechanism. The listener monitor verifies the listener process, and the
instance monitor verifies the functioning of the instance.
Oracle Clusterware or cluster manager (CM) is additional software that resides on top of a regular O/S that is
responsible for providing cluster integrity. A high-speed interconnect is used to provide communication between
nodes in the cluster. The Oracle Clusterware uses the interconnect to process heartbeat messages between nodes.
The function of the heartbeat messaging system is to determine which nodes are logical members of the cluster and to
update the membership information. The heartbeat messaging system enables the Oracle Clusterware to understand
how many members are in the cluster at any given point of time.
The CM

1. is a distributed kernel component that monitors whether cluster members can

communicate with each other;

2. enforces rules of cluster membership;

3. initializes a cluster, adds members to a cluster, and removes members from a cluster;

4. tracks which members in a cluster are active;

5. maintains a cluster membership list that is consistent on all cluster members;

6. provides a timely notification of membership changes;

7. detects and handles possible cluster partitions.

Oracle Clusterware discussed in the following is more robust compared to the traditional cluster managers: It has
many more components and provides more features, making a complete true cluster solution.

Oracle Clusterware Stack
At the cluster level, the main processes of the Oracle Clusterware provide standard cluster interface on all platforms
and perform high availability operations on each node in the cluster. Figure 2-4 illustrates the various processes that
compose the Oracle Clusterware stack.