Oracle 参数 DB_BLOCK_CHECKING 官方解释，作用，如何配置最优化建议
本站中文解释
DB_BLOCK_CHECKING 参数用于控制块检查的类型，其取值有如下：
1、TYPICAL: 使用MD5校验和基于CRC的检查，但不涉及比较相同空间中的多个块。
2、FULL: 将比较和计算同时作用于数据库实例中的所有字节，但仅在数据库实例启动时执行一次。
3、NULL->不进行块检查，后续会影响性能。
正确设置：
建议设置为 TYPICAL。
官方英文解释
DB_BLOCK_CHECKING specifies whether Oracle Database performs block checking for database blocks.
| Property | Description |
|---|---|
Parameter type | String |
Syntax |
|
Default value |
|
Modifiable |
|
Modifiable in a PDB | Yes, with the following restriction: If block checking is enabled for a CDB, then you cannot subsequently disable block checking in any of its PDBs. That is, if the value of |
Basic | No |
Values
OFForFALSENo block checking is performed for blocks in user tablespaces. However, semantic block checking for
SYSTEMtablespace blocks is always turned on.LOWBasic block header checks are performed after block contents change in memory (for example, after
UPDATE,INSERTorDELETEstatements, or after inter-instance block transfers in Oracle RAC).MEDIUMAll
LOWchecks and full semantic checks are performed for all objects except indexes (whose contents can be reconstructed by a drop+rebuild on encountering a corruption).FULLorTRUEAll
LOWandMEDIUMchecks 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 in most applications, 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.
Caution:
Before enabling block checking with this parameter, Oracle recommends that you detect and repair any logical corruptions in the database. Otherwise, a block that contains logical corruption will be marked as “soft corrupt” after block checking is enabled and the block is modified by a DML statement. This will result in ORA-1578 errors and the block will be unreadable. For more information about detecting and repairing logical corruptions, see Oracle Database Backup and
Recovery User’s Guide.
See Also:
Oracle Database
Administrator’s Guide for more information about this parameter
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