DB_BLOCK_CHECKING

最新推荐文章于 2025-12-10 22:03:01 发布

转载最新推荐文章于 2025-12-10 22:03:01 发布 · 125 阅读

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本文详细介绍了Oracle数据库参数DB_BLOCK_CHECKING的功能与使用方法。该参数用于控制数据库块的检查级别，防止内存和数据损坏。文章解释了不同设置（OFF、LOW、MEDIUM、FULL）对数据库块检查的影响及可能带来的性能开销。

Property Description
Parameter type String
Default value OFF
Modifiable ALTER SESSION, ALTER SYSTEM
Range of values OFF | LOW | MEDIUM | FULL
Basic No

DB_BLOCK_CHECKING controls whether or not Oracle performs block checking for
database blocks. The checking that is performed depends on the value you supply,
as follows:
■ OFF - no block checking is performed for blocks in the 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 RAC)
■ MEDIUM - all LOW checks are performed, as well as semantic block checking for
all non-index-organized table blocks
■ FULL - all LOW and MEDIUM checks are performed, as well as semantic checks
for index blocks (that is, blocks of subordinate objects that can
actually be dropped and reconstructed when faced with corruption)

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. 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.

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