Recovery - DBMS Questions and Answers

1.

If a transaction does not modify the database until it has committed, it is said to use the ___________ technique.

   A.) Deferred-modification
   B.) Late-modification
   C.) Immediate-modification
   D.) Undo

Answer: Option 'A'

Deferred modification has the overhead that transactions need to make local copies of all updated data items; further, if a transaction reads a data item that it has updated, it must read the value from its local copy.

2.

If database modifications occur while the transaction is still active, the transaction is said to use the ___________technique.

   A.) Deferred-modification
   B.) Late-modification
   C.) Immediate-modification
   D.) Undo

Answer: Option 'C'

We say a transaction modifies the database if it performs an update on a disk buffer, or on the disk itself; updates to the private part of main memory do not count as database modifications.

3.

The current copy of the database is identified by a pointer, called ____________ which is stored on disk.

   A.) Db-pointer
   B.) Update log
   C.) Update log records
   D.) All of the mentioned

Answer: Option 'A'

Any page which is not updated by a transaction is not copied, but instead the new page table just stores a pointer to the original page.

4.

In the ___________ scheme, a transaction that wants to update the database first creates a complete copy of the database.

   A.) Shadow copy
   B.) Shadow Paging
   C.) Update log records
   D.) All of the mentioned

Answer: Option 'A'

If at any point the transaction has to be aborted, the system merely deletes the new copy. The old copy of the database has not been affected.

5.

The log is a sequence of _________ recording all the update activities in the database.

   A.) Log records
   B.) Records
   C.) Entries
   D.) Redo

Answer: Option 'A'

The most widely used structure for recording database modifications is the log.

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