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    Understanding Clusterware of RAC

    The blog post explains about what is the clusterware of Oracle RAC and how each components are working in RAC to provide best performance.

    Clusterware Components:

    The main important component of a cluster is cluster nodes. You have to have a cluster node before you can create a cluster. A cluster node is the central point of the cluster, and it can process requests from other cluster members. The node is responsible for all of the processing for the cluster and the resources are shared among all members of the cluster.

    Your cluster should have the same hardware, configuration, and information so that you can run the same software. If you try to deviate from this, you will have performance issues and the same operating system configuration as we have today. If you want to create a cluster with multiple OS clustering solutions, you need to install Linux on the first node and Windows on the second, and then install Clusterware software.

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    The best solution for this problem is to use the same operating system on all of the nodes. It’s probably going to be Oracle at some point, but for now, it’s not specific to the application team. It’s related to our database software or the clusterware software. So basically, each node will have the clusterware software each node will have the Oracle_home installed over there. So that’s why this is not related to the application team. It is related to our Oracle database and Grid software. You’ll need to install the ORACLE_HOME on each node.

    You can’t have one node installation and then continue. The second component of the cluster is nothing but our clusterware software, without which the multiple nodes cannot work as one node. It is the software that makes the cluster it’s not the nodes that become clusters automatically. It is the clusterware software that makes them a cluster and it manages the workload as we have already seen in our last session. It is the job of clusterware software to distribute the incoming connections to the nodes. The job of clusterware software is to maintain a repository where it knows that. Ok, what is the load on node 1? What is the load on the node, 2 and depending on the load, the new incoming connections are given to the particular node and even let’s take your node one is down. Then the Clusterware software is responsible for pushing the new connections

    Let’S say your nodes are evicted if there is a term that is used in RAC, that is node

    How will clusterware software be able to provide high availability? The meaning of node eviction is sometimes your nodes will go out of the cluster. Now it’s the job of the clusterware software to restart the node and join them back into the cluster. That’s how clusterware software will manage the nodes, and there are a few things that will understand in the clusterware architecture, where you will understand how Clusterware software manages the nodes, so the clusterware software is responsible for providing high availability. So how does it perform or provides high availability? Let’s take, there are 10 nodes in the cluster and 9 nodes are down. If a user sends a request, the Clusterware software will try to check with node one it’s down.

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    It will check with node two it’s down. This is why we need cluster technology. It is very complex but it’s not impossible to understand and it will take three and continue till nine, and after nine it won’t revert back to the user. Saying that nodes are down, it will try its best with every possible node and we have the tenth node live in the cluster and the Clusterware software will get it executed over there and give the results to the user. So that way, the Clusterware software provides high availability, It never reboots back to the user, saying that boss, your request, landed on node, 1 and node 1 is down. We cannot help. This is how your Clusterware software basically provides high availability.

    A cluster is a single group of machines that are connected to each other. The group is named in such a way that it appears to outsiders as one big machine. Clusters are grouped together based on how they are used, and how their performance affects the overall system.

    You do not give any IP address, you do not give any local or physical name of each node. You just give a cluster’s name. The clusterware software will then allocate the work. So let us look at this point. What and how the user connection happens in RAC we’ll talk later, Let us understand the cluster working in a generic term. These are your user connections. Your users are connecting to the cluster So on any cluster or wherever you install the clusterware software. Let’S take you have installed the clusterware software on four nodes: All these nodes are connected and they are speaking to the shade storage as well.

    So, whatever customers try to connect to your cluster, they will have a cluster name.Let’s take This is the cluster name. The clients will send their queries to this cluster name, and this cluster name is basically assigned to your Clusterware software.Once the client request comes to this clusterware name, the job of the Clusterware software or the grid, software in our case would be to allocate the work to the respective nodes.

    The best part about the Clusterware software is, it knows the load on each node, and then it will try to send the work or allocate the work to the particular nodes. The Clusterware software is nothing, but the grid is the one that basically gives work to your nodes. It is not. The client will never directly interact with the node Client will just send a request to a name, the cluster name, or a hostname, and that name is nothing but your Clusterware software name. The Clusterware software will then decide by itself where to send this request. The same way happens in the response time.

    This is a very generic scenario, where the work is given to one node. Node one has a database instance that talks to the shared storage. It gets the blocks into the instance and then returns the blocks to the user.

    Working on clustering software:

    So this is the reason for the outside world. Whatever applications you have, it will have only one connection name now. The application does not know that whether this is a single host, whether this is a RAC software, whether this is a cluster, or whether it is one server one single desktop nothing. The outside world is just bothered to send their queries to this particular name and from this name, the work is done So why it is called highly scalable because, let’s take that even though my cluster is up and running, I can add nodes to the cluster. Again and again, without impacting the existing cluster and without impacting the users.

    I will remove a few nodes, but I can also take it down. When I remove the nodes from the cluster, my clusterware knows that node three is no longer available. The only node is one, so I won’t give it any work.

    and node two with you to get the work done. So clusterware software will allocate work to node one and node two. When you add nodes to the cluster, then your cluster ware software is smart enough. Ok, we have 2 more nodes. So next time new connections will come, we will give it to node three and node four. So that is why cluster ware software’s job is to manage the entire work within the cluster.

    And finally, Oracle Next cluster software has been developed by Oracle Next cluster component. We know the importance of shared storage and if you do not have shared storage, we will be getting into trouble called no dependency. So, let’s take if you install an entire database on the node, 1 and other nodes are connecting to node 1, then it becomes a node.

    If something happens to your node 1, you cannot access your database. So RAC is the share everything architecture. And how can you share If you put things on shade storage, It removes single node dependency and is accessible by all nodes, multi-node, read/write permissions Access volume manager and file system pick. What is the volume manager? What is the file system, and all this will be addressed when we are under ASM topic, so for now just understand that shade storage is the area where we push all the files and every node can access it.

    Administers redundancy. Okay manages storage. This includes disk groups, Oracle RAC, the shade of everything architecture. These three points that we have. This is more related to Oracle ASM, so I won’t talk about them right now. And finally, the networks. We are pretty much good with the network. Each node must be connected to a network minimum of two or more local area networks recommended see. It depends on the cluster. Some clusters might require more than two networks also, they might require two private networks. When we say two private networks, one private network for inter-node communication and another private network for shared storage, communication, it depends on the cluster to cluster, but Oracle RAC needs only two networks Which is virtual IP scan IP.

    We will be focusing on the two networks that we have been working on so far when we are in the networking configuration so for now. I won’t talk about virtual IP scan, IP scan, listeners, or local node listeners because we are focused on the cluster component, So I am trying to keep things as simple as possible because I don’t want to confuse you guys at the initial stage.

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