Oracle 12c New Feature -- Oracle Flex Clusters

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Blog | Aug 26, 2016

Oracle 12c New Feature -- Oracle Flex Clusters

One benefit of running the loosely coupled architecture of the Flex Cluster is to provide the high availability of the Oracle Cluster-ware of the applications tier.

In my maiden blog I would like to introduce a relevantly new feature of Oracle 12c Cluster database i.e. Oracle Flex Clusters which has some impressive functionalities.

Before getting into the details of this new feature, let’s start with a review of 11gR2 cluster first. 11gR2 cluster is also referred to as a tightly or Standard connected cluster architecture.

  1. Each node in the cluster is connected to other nodes through the private interconnect.
  2. Each node in the cluster is directly connected to the shared storage.

The 11gR2 architecture presents significant technical challenges and performance overhead if clusters need to be scaled out to many more nodes than most clusters today. 

One issue is a dramatic increase of the interconnect traffic between cluster nodes.

In a standard cluster we can calculate the possible interconnect paths for cluster heartbeats and data exchanges between the nodes by the formula “N *(N-1)/2”.

Here we can understand it by an example, suppose a 16-node standard cluster needs to be setup and then we need 120 different interconnect paths and 16 storage connections. It may be manageable but if we scale this cluster to 500-node then it requires 124,750 interconnect paths and 500 storage connections. Now we can imagine how it is complex and very difficult to manage. It also affects the overall cluster performance, it is obvious that this standard connected cluster architecture prevents the cluster from being scaled further. 

Intro to Oracle 12c Flex Clusters:
Oracle 12c Flex Clusters are designed to tackle the above limitation by introducing a new two-layered hub-and–spoke topology to the cluster architecture. This new cluster consists of two types of nodes: Hub nodes and Leaf nodes.

Hub Nodes:
The group of Hub nodes is tightly connected as the nodes in the standard cluster in Oracle RAC 11gR2: all the Hub nodes are connected with each other through the private interconnects and they also are directly connected to the shared storage through the physical storage network connections. 

Leaf Nodes:
Leaf nodes are not connected to each other like Hub nodes. Leaf nodes also do not require direct access to the storage. There is no direct communication between Leaf nodes. Instead, each Leaf node communicates with its attached Hub node exclusively and is connected to the cluster through its Hub node. Leaf nodes get data through the attached Hub node.

Oracle Flux architecture.

oracle system architecture support

 Image Source:

In this example, there are four Hub nodes in the Hub center that form the hub of the cluster similar to a standard cluster supported in Oracle 11gR2 Cluster-ware. These four Hub nodes are tightly connected with the private interconnect, which is the same as the one in the standard Oracle 11g R2 cluster. All of these Hub nodes are also required to have direct access to the shared storage, which stores the database files as well as the Oracle Cluster Registry (OCR) and the voting disks for the Oracle Clusterware. The database instances running on their Hub nodes will function in the same way as in a standard cluster. 

Outside of the Hub center, 12 Leaf nodes form four groups. Each group of Leaf nodes is connected to one Hub node, which is the attached node for all the Leaf nodes in the group. None of the Leaf nodes are connected to any other Leaf nodes in the cluster. Oracle RAC database instance can also run on Leaf nodes. Since these Leaf nodes do not have direct access to the shared storage, the RAC database instances on the Leaf nodes will need to get the database through the Hub nodes. 

One benefit of running the loosely coupled architecture of the Flex Cluster is to provide the high availability of the Oracle Cluster-ware of the applications tier. Also architectural differences between standard cluster to flex cluster. Please stay tuned for next blog where will discuss implementation of Oracle Flex Clusters. For any questions on the features click below:

Ask Mukesh