Checksums can be used to check the integrity of database disk I/O operations. A checksum is a calculated numeric value computed from a given set of data, or specific portions of the data. For a given set of data, the checksum value will always be the same, provided the data is unchanged.
Checksums can be used to detect when there are errors in disk I/O operations. When checksums are enabled, and data is initially read, a checksum is calculated for the data and stored in the system. When the same data is subsequently read, the checksum is recalculated and compared to the original checksum value. Differing checksum values for a given set of data indicate an inconsistency in the data, most often due to errors in disk I/O operations.
- System Journal
- System Logging
- Permanent Journal
These table classes are described in the sections that follow.
Because calculating checksums requires system resources, and may affect system performance, the checksum feature is disabled by default on most platforms, but can be enabled by the Teradata Support Center if disk corruption is suspected.