15.00 - Primary Index Uniqueness and Row Distribution - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Primary Index Uniqueness and Row Distribution

The singularity of the primary index for a table is directly related to how evenly table rows are distributed across the AMPs. The more singular the index, the more optimal the use of disk space, with primary index uniqueness producing the most efficient space utilization. Because primary indexes are a component of base table rows, they do not require subtables or any other disk space beyond that required to store the primary index column data in the base table row.

The following mini-case studies illustrate how the degree of singularity of the values in the column selected to be the primary index for a table affects the distribution of rows across the AMPs.

The examples use the following customer table as their basis. Assignment of the primary index varies from case to case. Only a small sample of table rows is shown. Assume a 6‑AMP system.