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 |
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Default value |
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Modifiable |
|
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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 |
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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
