What index provides the most uniform data distribution in Teradata?

The Unique Primary Index is designed to ensure that each row within a table has a distinct identifier, which leads to a more uniform distribution of data across the AMPs (Access Module Processors) in Teradata. When a Unique Primary Index is defined on a table, Teradata automatically hashes the values of the indexed column(s) to determine the optimal storage location for each row. This hashing process helps to evenly distribute rows across the available AMPs, minimizing the likelihood of data skew.

A uniform data distribution is crucial for achieving optimal performance during query execution because it allows for balanced workload distribution across AMPs, leading to efficient data retrieval and manipulation. If data were unevenly distributed, some AMPs would have to handle more data than others, resulting in longer query execution times and potential bottlenecks.

In contrast, a Nonunique Primary Index may result in multiple rows being directed to the same AMP if there are duplicate values in the indexed columns, which could lead to data skew. Secondary Index and Join Index serve different purposes; secondary indexes provide alternative paths to access data without impacting the primary distribution, while join indexes are designed for simplifying joins, but they do not primarily focus on data distribution.