Recovery System

Question 1

Three Types of Failure Classification

Answer 1

1. Transaction Failure
2. System Crash
3. Disk Failure

Question 2

Two types of Transaction Failures

Answer 2

1. Logical errors- transaction cannot complete due to internal error condititon
2. System errors- system must terminate a transaction due to error condition (deadlock)

Question 3

What happens in deferred modification?

Answer 3

If a transaction does not modify the database until it has committed.

With deferred modification, log records do not need
to contain old values of updated data items.

Deferred modification has the overhead that transactions need
to make local copies of all updated data items;

Question 4

What happens in immediate modification?

Answer 4

Database modifications
occur while the transaction is still active

Question 5

When do we undo a record in log?

Answer 5

Log has <Ti>, but does not contain the record <Ti>.</Ti></Ti>

Question 6

When do we redo a record in log?

Answer 6

log contains both the record <Ti> and the record <Ti>.</Ti></Ti>

Question 7

Explain the purpose of checkpoint

Answer 7

Reduce Recovery Time: Checkpoints allow the system to determine which transactions need to be redone or undone after a crash without searching the entire log.

Minimize Overhead:Checkpoints help minimize this overhead by providing a reference point for determining which transactions need to be redone.

Optimize Recovery Process: Checkpoints enable the system to streamline the recovery procedure by identifying the set of transactions active at the time of the crash. This helps in efficiently applying redo and undo operations only to the necessary transactions.

Question 8

How does the frequency of checkpoints affect System performance when no failure occurs?

Answer 8

When no failure occurs, the frequency of checkpoints directly impacts system performance. More frequent checkpoints can lead to increased overhead due to the interruption of regular transaction processing for checkpoint operations. This interruption can result in decreased throughput and longer response times for user transactions. On the other hand, less frequent checkpoints reduce the overhead associated with checkpointing but may lead to longer recovery times in the event of a failure. Therefore, finding the right balance in checkpoint frequency is crucial