Duplicate copy protection for the table.
When you specify FALLBACK, Teradata Database creates and stores duplicate copies of rows in the table.
The default for this option is set by a CREATE DATABASE, CREATE USER, MODIFY DATABASE, or MODIFY USER request for the database in which the table is to be created.
When a hardware read error occurs, the file system reads the fallback copy of the data and reconstructs the rows in memory on their home AMP. Support for Read From Fallback is limited to the following cases:
- Requests that do not attempt to modify data in the bad data block
- Primary subtable data blocks
- Reading the fallback data in place of the primary data. In some cases, Active Fallback can repair the damage to the primary data dynamically. In situations where the bad data block cannot be repaired, Read From Fallback substitutes an error-free fallback copy of the corrupt rows each time the read error occurs.
- Duplicate copy protection is not provided for the table.You cannot use the NO FALLBACK option and the NO FALLBACK default on platforms optimized for fallback.
- Optional keyword that can be specified after the FALLBACK keyword.