Case Study 2: Highly Nonunique Primary Index Values
This study defines a NUPI on customer_status. Because there are only two distinct values for this attribute (Active and Inactive), all rows hash to two AMPs, leaving the other four AMPs in the system unaffected by the customer table.
Distributions that are skewed like this cause major performance problems because they fail to harness the powerful parallel processing capabilities that make Teradata unique among commercially available relational database management systems.
The illustration shows the customer table rows stored on only two AMPs.