OCP-1Z0-053-V13.02-400题

400.Which of the following methods can be used to detect block corruption?

A. ANALYZE operations

B. dbv

C. SQL queries that access the potentially corrupt block

D. RMAN

E. All of the above

Answer: E

答案解析：

参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmblock.htm#BRADV89783

Identification of Corrupt Blocks

The V$DATABASE_BLOCK_CORRUPTION view displays blocks marked corrupt by database components such as RMAN, ANALYZE, dbv, and SQL queries. The following types of corruption result in the addition of rows to this view:

• Physical corruption (sometimes called media corruption)

  The database does not recognize the block: the checksum is invalid, the block contains all zeros, or the block header is corrupt.

  Physical corruption checking is enabled by default. You can turn off checksum checking by specifying the NOCHECKSUM option of the BACKUP command, but other physical consistency checks, such as checks of the block headers and footers, cannot be disabled.

• Logical corruption

  The block has a valid checksum, the header and footer match, and so on, but the contents are logically inconsistent. Block media recovery may not be able to repair all logical block corruptions. In these cases, alternate recovery methods, such as tablespace point-in-time recovery, or dropping and re-creating the affected objects, may repair the corruption.

  Logical corruption checking is disabled by default. You can turn it on by specifying the CHECK LOGICAL option of the BACKUP, RESTORE, RECOVER, and VALIDATEcommands.

The database can detect some corruptions by validating relationships between blocks and segments, but cannot detect them by a check of an individual block. The V$DATABASE_BLOCK_CORRUPTION view does not record at this level of granularity.