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DB_BLOCK_CHECKING

Property Description
Parameter type String
Syntax DB_BLOCK_CHECKING = { FALSE | OFF | LOW | MEDIUM | TRUE | FULL }
Default value FALSE
Modifiable ALTER SYSTEM
Basic No

DB_BLOCK_CHECKING specifies whether or not Oracle performs block checking for database blocks.

Values:

  • OFF or FALSE

    No block checking is performed for blocks in user tablespaces. However, semantic block checking for SYSTEM tablespace blocks is always turned on.

  • LOW

    Basic block header checks are performed after block contents change in memory (for example, after UPDATE or INSERT statements, on-disk reads, or inter-instance block transfers in Oracle RAC).

  • MEDIUM

    All 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).

  • FULL or TRUE

    All LOW and 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 DB_BLOCK_CHECKING to FULL if the performance overhead is acceptable.

For backward compatibility, the use of FALSE (implying OFF) and TRUE (implying FULL) is preserved.