The hash index uses fallback protection.
The default is to use the fallback specification for the database in which the hash index is defined.
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.
The hash index does not use fallback protection.
If a hash index is not fallback protected, an AMP failure prevents the following events from occurring:
- Processing queries on the hash index
- Updating the table on which the hash index is defined