Physical Database Design - High-Performance Web Databases: Design, Development, and Deployment - page 344

Exhibit 21-10. Hashing search keys.

A hashed index works basically the same way as a hashed
file. A hashing function is applied to the value of the search key to calculate
the number of the data page for the search key value. As illustrated in
Exhibit 10a, if the search key is the same as the primary search key used for
a hashed file, then no additional structure is needed. However, if the search
key is different from the primary search key used for the hashed file as
shown in Exhibit 10b, then a linking table is needed to relate the address
calculated by the hashing function and the actual data page used by the
underlying hashed file. Exhibits 10c and 10d show that a linking table is
needed to relate the address calculated by the hashing function with the
actual data page used by the underlying sorted or heap file.

Hashed Index.