Database Reference
In-Depth Information
exeRCiSe 9.2 (continued)
ADR Home = c:\TEMP\diag\tnslsnr\CPACK042\listener:
*************************************************************************
0 rows fetched
adrci> EXIT //or QUIT
You can use the ADRCI utility PURGE command to manually purge expired
diagnostic data.
Performing Block Media Recovery
Block media recovery (BMR) is used to repair corrupt blocks within a data file. It allows you
to recover corrupt blocks while keeping the data file online, as opposed to data file media
recovery, which requires taking the file offline during the restore and recovery operation. You
can perform BMR only on blocks that are identified as corrupt. Block media recovery requires
the Enterprise Edition of Oracle Database 12 c .
Advantages of Block Media Recovery
The advantages of block media recovery are straightforward:
The mean time to recovery (MTTR) is reduced.
Data files remain online while corrupt blocks are repaired.
These advantages are related to recovery performance and returning the customer to
normal operating mode.
Detecting Block-Level Corruption
Data-block corruption can occur because of memory corruption that is written to disk or
because of I/O errors. Corruption is detected by dbv , SQL that accesses corrupt blocks,
RMAN, ANALYZE operations, and any other operation that attempts to read data from a
corrupt block, including DBMS_REPAIR.CHECK_OBJECT . Once a corrupt block is detected,
the database will not allow access to that block until it is repaired.
Physical and logical block corruption are recorded in V$DATABASE_BLOCK_CORRUPTION .
Physical block corruption occurs when the database does not recognize the block because
the block header is damaged, the checksum is invalid, or the block contains all zeros. This is
often due to disk hardware or OS failures and often is not acknowledged as corruption by the
OS or underlying storage devices. Logical block corruption occurs when the contents of the
block are logically inconsistent, sometimes the result of an Oracle internal error. Logical block
 
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