Which three are true about corrupted data blocks and their recovery in an Oracle Database?

Question

Options

• AIf a row lock is held by a nonexistent transaction, the block containing the row is media corrupt.
• BDB_BLOCK_CHECKING=TRUE causes a check sum to be added to each data block to help
• CA media corrupt block is one where the block is not formatted correctly.
• DThe ANALYZE TABLE VALIDATE STRUCTURE CASCADE command verifies that each table
• EIf a row lock is held by a nonexistent transaction, the block containing the row is logically
• FDB_LOST_WRITE_PROTECT=TYPICAL causes extra logging overhead on the standby

• A
  9% (2)
• B
  5% (1)
• C
  5% (1)
• D
  82% (18)

Explanation

D, E, and F are correct because they accurately describe Oracle's corruption taxonomy and protection mechanisms.

D is correct: ANALYZE TABLE VALIDATE STRUCTURE CASCADE is a genuine Oracle command that checks internal consistency of a table and its indexes - walking every row and verifying corresponding index entries - making it a valid tool for detecting logical corruptions.

E is correct: A row lock held by a nonexistent transaction (an ITL entry pointing to a transaction no longer in the undo segments) is the textbook definition of logical corruption - the block's physical format is intact, but its data state is semantically inconsistent.

F is correct: DB_LOST_WRITE_PROTECT=TYPICAL works by recording extra block-level SCN information in redo, enabling the standby to detect when a primary write was "lost." This additional redo logging does introduce overhead.

Why the distractors fail:

• A misidentifies the corruption type - a stale row lock is logical, not media corruption.
• B confuses two different parameters: DB_BLOCK_CHECKING=TRUE performs internal structure checks, but it is DB_BLOCK_CHECKSUM that adds checksums to blocks.
• C gets the definition backwards - media (physical) corruption means the block failed a checksum or I/O validation, not simply that it is "not formatted correctly" (which better describes an uninitialized block).

Memory tip: "Locks = Logical, Disk = Media, Checking ≠ Checksum." If data is internally inconsistent (like a phantom lock), it's logical. If the physical block itself is unreadable, it's media. And always remember: DB_BLOCK_CHECKING checks; DB_BLOCK_CHECKSUM signs.

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