The DEFAULT CLUSTER command indicates that Configuration is to assign AMPs to clusters automatically for the specified configuration.
An AMP cluster is a collection of AMPs that are grouped together logically to provide fallback capability for each other for tables that are created with the FALLBACK option. Each AMP in a cluster contains a backup copy of a portion of the primary data for every other AMP in the cluster.
Syntax element …
the default cluster size.
The maximum value of c is 8. If you do not specify a default cluster size, the default size is 2.
Typically, you type the DEFAULT CLUSTER command at the end of a session during which AMPs were added to the system.
When the DEFAULT CLUSTER command is executed, AMPs are assigned to clusters automatically.
In a system with n AMPs, each cluster contains c AMPs and n/c clusters.
If n is not divisible by c, the last cluster will be no smaller than 50% less and not larger than 50% more than any other cluster. The number of clusters is adjusted accordingly.
After the DEFAULT CLUSTER command is accepted, AMPs are assigned to clusters, and the system displays:
The cluster assignment is complete.
Execution of the DEFAULT CLUSTER command overrides all previous cluster assignments.
AMP cluster assignments should be defined with respect to the hardware configuration. Usually, AMP failures result from hardware-related problems. AMP clustering assignments should be defined as closely as possible to the following fault-tolerant strategy:
DEFAULT CLUSTER 4 for a system of 15 AMPs results in a cluster size of 4. Two clusters include 4 AMPs
each, and 1cluster includes 7 AMPs.
DEFAULT CLUSTER 3 for a system of 16 AMPs results in cluster size of 3. Four clusters include 3 AMPs
each, and 1 cluster includes 4 AMPs.
DEFAULT CLUSTER 8 for a system of 16 AMPs results in a cluster size of 8. Two clusters include 8 AMPs