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A clique is a set of Teradata nodes that share a common set of disk arrays which are connected in daisy chain network to each disk array controller.
Clique is mainly used to prevent node failures. Group of nodes which share common disk drives is called CLIQUE.
Group of cylindrical or physical disks arranged in array fashion is called VDISKS.
After AMP performing the operations it invokes the controllers to store and manage the data across physical disks.
Here the two controllers are active and they do the same operation so we call this controllers as DUAL REDUNDANT ACTIVE ARRAY CONTROLLERS.
AMP, acronym for “Access Module Processor,” is the type of vproc (Virtual Processor) used to manage the database, handle file tasks and and manipulate the disk subsystem in the multi-tasking and possibly parallel-processing environment of the Teradata Database. AMP contains Database Management Subsystem and it performs below operations:
In the event of a node failure, cliques provide for data access through vproc migration. When a node resets, the following happens to the AMPs:
Vprocs are distributed across all nodes in the system. Multiple cliques in the system should have the same number of nodes.
The diagram below shows three cliques. The nodes in each clique are cabled to the same disk arrays. The overall system is connected by the BYNET. If one node goes down in a clique the vprocs will migrate to the other nodes in the clique, so data remains available. However, system performance decreases due to the loss of a node. System performance degradation is proportional to clique size.
This node is not functional till any other node goes down, simply acts like an extra player. In a clique,multiple nodes are accessible by any node in the same clique. The facing page shows a situation where a node fails. When the node fails PDE resets and Teradata restarts and the amp vprocs migrate to the other nodes in the clique.