What is a clique?
- A clique is a set of Teradata nodes that share a common set of disk arrays that are connected in a daisy chain network to each disk array controller.
- Clique is mainly used to prevent node failures. A group of nodes that share common disk drives is called CLIQUE.
- A 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 these controllers as DUAL REDUNDANT ACTIVE ARRAY CONTROLLERS.
What is meant by AMP in Teradata?
AMP, an acronym for "Access Module Processor," is the type of vproc (Virtual Processor) used to manage the database, handle file tasks 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 the below operations:
- DDL
- DML
- Applying and releasing the locks
- Joins, aggregations, etc
A logical disk, logical volume, or virtual disk (VD or vdisk for short) is a virtual device that provides an area of usable storage capacity on one or more physical disk drive(s) in a computer system.
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What is the Teradata database?
Teradata is a relational database management system (RDBMS) that is: Teradata is an open system, running on a UNIX MP-RAS or Windows server platform. Teradata is capable of supporting many concurrent users from various client platforms. Teradata is compatible with industry standards (ANSI compliant).
Cliques provide data accessibility if a node fails for any reason, Proms are distributed across all nodes in the system. Large multiple node systems will have clique mechanisms associated with them
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:
- When the node fails, the Teradata Database restarts across all remaining nodes in the system.
- The vprocs (AMPs) from the failed node migrate to the operational nodes in its clique.
- The PE vprocs will migrate as follows: LAN attached PEs will migrate to other nodes in the clique. Channel attached PEs will not migrate. While that node remains down, that channel connection is not available.
- Disks managed by the AMP remain available and processing continues while the failed node is being repaired.
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 the clique size.
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BYNET (Banyan Network)
It acts as the "Message Communication" layer between components.
- SMP BYNET [PE-AMP]
POINT-POINT: One msg from PE - One Amp
MULTICAST: One msg from PE- Many Amps
BROADCAST: One msg from PE - All Amps
2. MPP BYNET [NODE-NODE]
POINT-POINT: One msg from One Node to Another Node
MULTICAST: One msg from One Node to Many Node
BROADCAST: One msg from One Node to All Nodes
MULTIPLE CLIQUES IN SYSTEM (OR) HIGH LEVEL
INSIDE CLIQUE PROCESS(OR)SINGLE CLIQUE:-
If Node, fails
Every multi-system environment will have multiple cliques, each clique contains an equal number of nodes.
Clique is nothing but group of nodes sharing common disk drives here the advantage is if any node goes down the virtual process migrate to other nodes to perform the operation.in this way, it provides high availability of data even node goes down.
HSN (HOT STAND by NODE)
- This node is not functional till any other node goes down, simple 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.
- A massively parallel processing system will continue to run if a node or disk fails in the clique, even if you do not select the fallback option in the situation shown the TDP will restart the lost amp vprocs on different nodes within the clique. When the node is brought back to its original node for 7x24 systems, the fallback option is recommended for minimizing the risks of the system down time.
- Applications that recognize restarts and are coded to will continue when the system comes back up otherwise, applications will need to be restarted.
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