Database Reference
In-Depth Information
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Cluster Health Monitor (CHM) Enhancements
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Windows: Support for Oracle Home User
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Introducing Application Continuity
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Transaction Idempotence and Java Transaction Guard
Oracle Flex Clusters
Oracle Flex Cluster Architecture
As stated in Chapter 1, previous releases of Oracle Clusterware such as 11gR2 and earlier supported only the tightly
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.
This architecture will present significant technical challenges and performance overhead to cluster scalability if
the cluster needs to be scaled out to many more nodes that most clusters today.
One issue is a dramatic increase of the interconnect traffic between cluster nodes. In a tightly connected
cluster which we can call the standard cluster, since the interconnect connects each pair of nodes and every node
is connected to the shared storage, an N-node cluster will have N *(N-1)/2 possible interconnect paths for cluster
heartbeats and data exchanges between two nodes and N connection paths to the shared storage.
In a small or modestly sized cluster such as a 16-node cluster, 120 different interconnect paths and 16 storage
connections may still be manageable. However, if we want to scale a cluster to a much bigger scope, for example 500
nodes, it will have 124,750 interconnect paths and 500 storage connections. Not only the complexity of the number of
interconnect paths and storage connections makes the cluster very difficult to manage, the network traffic overhead
due to this extremely high number of interconnect paths will practically impact the cluster performance hugely. It is
obvious that this tightly connected cluster architecture prevents the cluster from being scaled further.
Oracle 12c Flex Clusters are designed to tackle this 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. 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 each other through the private interconnects and they also are directly connected to the shared storage
through the physical storage network connections.
On the other hand, Leaf nodes run a lighter-weight stack and they 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. The cluster heartbeats for Leaf nodes only
occur between Leaf nodes and their attached Hub nodes.
Now let's use a 16-node cluster as an example to show the two-layered hub-and-spoke topology of an Oracle Flex
Cluster in Figure
4-1
.
