Row Distribution
Teradata rows are hashed across the AMPs of a system using the row hash value of their primary index or primary AMP index as the hash key. This does not apply for the rows of NoPI tables. See “Row Assignment for NoPI Tables” on page 185 and “Row Assignment for FastLoad Operations Into Nonpartitioned NoPI Tables” on page 186 for details.
Teradata Database also uses the row hash of a primary index or primary AMP index to retrieve a row. The following graphic shows how a row is hashed and assigned to an AMP:
By carefully choosing the primary index or primary AMP index for each table, you can ensure that rows that are frequently joined hash to the same AMP, eliminating the need to redistribute the rows across the BYNET in order to join them.
The following graphic shows how you can set up rows from commonly joined tables on the same AMP to ensure that a join operation avoids being redistributed across the BYNET:
