|Oracle® Database Reference
11g Release 2 (11.2)
|PDF · Mobi · ePub|
DB_BLOCK_CHECKING specifies whether or not Oracle performs block checking for database blocks.
No block checking is performed for blocks in user tablespaces. However, semantic block checking for
SYSTEM tablespace blocks is always turned on.
Basic block header checks are performed after block contents change in memory (for example, after
INSERT statements, on-disk reads, or inter-instance block transfers in Oracle RAC).
LOW checks and full semantic checks are performed for all objects except indexes (whose contents can be reconstructed by a drop+rebuild on encountering a corruption).
MEDIUM checks and full semantic checks are performed for all objects.
Oracle checks a block by going through the data in the block, making sure it is logically self-consistent. Block checking can often prevent memory and data corruption. Block checking typically causes 1% to 10% overhead, depending on workload and the parameter value. Specific DML overhead may be higher. The more updates or inserts in a workload, the more expensive it is to turn on block checking. You should set
FULL if the performance overhead is acceptable.
For backward compatibility, the use of
FULL) is preserved.