what is server side load balancing in RAC and how does it happen?

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 In a Real Application Clusters (RAC) environment, server-side load balancing refers to the ability to distribute client connections across multiple database instances (or nodes) in the cluster. This ensures that the workload is evenly distributed among the nodes, which can improve performance and scalability.


Server-side load balancing is achieved through the use of a load balancing advisory, which is a set of algorithms that determine the most appropriate node for a particular client connection. The advisory takes into account various factors such as the current workload, available resources, and the location of the data being accessed.


When a client connects to the RAC cluster, the connection request is intercepted by the Oracle Net listener, which then forwards the request to one of the available nodes based on the load balancing advisory. The node chosen by the advisory becomes the connection's primary instance, which is responsible for managing the client's session and coordinating access to shared resources (such as datafiles and control files) across the cluster.


If the workload on the primary instance becomes too high, the load balancing advisory can switch the connection to a different node in the cluster. This ensures that the workload is balanced across the cluster and that no single node becomes overloaded.


Here's an example to illustrate how server-side load balancing works in RAC:


Suppose you have a RAC cluster with three nodes (Node 1, Node 2, and Node 3) and a client application that connects to the database using a service named "sales_service". When the client application makes a connection request, it is intercepted by the Oracle Net listener on one of the nodes (say, Node 1).


The load balancing advisory on Node 1 determines that Node 2 has the least amount of workload and is the best candidate for handling the connection. The listener on Node 1 then forwards the connection request to the listener on Node 2, which creates a new session for the client.


If the workload on Node 2 increases and becomes too high, the load balancing advisory can switch the connection to Node 3, which has more available resources. This ensures that the workload is balanced across the cluster and that no single node becomes overloaded.


In summary, server-side load balancing in RAC involves distributing client connections across multiple nodes in the cluster using a load balancing advisory that takes into account various factors such as workload and resource availability.

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