Solution

The correct answer is C. D. A. B.

Key Points

• The sequence of steps for executing a write-item (X) command in transactions is crucial to ensure data integrity and consistency.
• The correct order, C. D. A. B, ensures that the disk block containing the item is identified, loaded into the buffer, updated with the new value, and then saved back to the disk.
• Each step builds upon the previous one to complete the write operation effectively.
• Skipping or misordering these steps may lead to incomplete or incorrect updates in the database.

Additional Information

• Step-by-Step Sequence Explanation:
  • C: Find the address of the disk block that contains the item. This step is necessary to locate the specific block where the item resides.
  • D: Copy the disk block into a buffer in main memory. This ensures the block is accessible for modification.
  • A: Update the item in the buffer by copying the program variable's value into its correct location. This step modifies the data as required.
  • B: Write the updated block from the buffer back to the disk. This completes the write operation by saving the changes permanently.
• Why this sequence is important:
  • Ensures that data is correctly updated without corrupting existing records.
  • Prevents loss of changes by writing the updated block back to disk.
  • Maintains the consistency of the database during transactions.