15.00 - Sizing a Reference Index Subtable - Teradata Database

Teradata Database Design

Teradata Database
User Guide

Sizing a Reference Index Subtable

A reference index is an internal structure that the system creates whenever a referential integrity constraint is defined between tables using a PRIMARY KEY or UNIQUE constraint on the parent table in the relationship and a REFERENCES constraint on a foreign key in the child table.

The index subtable row contains a count of the number of references in the child, or foreign key, table to the PRIMARY KEY or UNIQUE constraint in the parent table.

A maximum of 64 referential constraints can be defined for a table.

Similarly, a maximum of 64 other tables can reference a single table. Therefore, there is a maximum of 128 reference indexes that can be stored in the table header per table.

The limit on reference indexes in the table header includes both references to and from the table and is derived from 64 references to other tables plus 64 references from other tables to the current table = 128 reference index descriptors.

However, the maximum number of reference indexes stored in the reference index subtable for a table is limited to 64, defining only the relationships between the table as a parent with its child tables.

Estimate the size of your reference indexes using the equation provided in Reference Index Sizing Equation.