DB_BLOCK_CHECKSUM determines whether DBWn and the direct loader will calculate a checksum (a number calculated from all the bytes stored in the block) and store it in the cache header of every data block when writing it to disk. Checksums are verified when a block is read-only if this parameter is true and the last write of the block stored a checksum. In addition, Oracle gives every log block a checksum before writing it to the current log.
If this parameter is set to false, DBWn calculates checksums only for the SYSTEM tablespace, but not for user tablespaces.
Checksums allow Oracle to detect corruption caused by underlying disks, storage systems, or I/O systems. Turning on this feature typically causes only an additional 1% to 2% overhead. Therefore, Oracle Corporation recommends that you set DB_BLOCK_CHECKSUM to true.
DB_BLOCK_CHECKING controls whether Oracle performs block checking for data blocks. When this parameter is set to true, Oracle performs block checking for all data blocks. When it is set to false, Oracle does not perform. block checking for blocks in the user tablespaces. However, block checking for the SYSTEM tablespace is always turned on.
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