Explain the purpose of the checkpoint mechanism. How often should checkpoints be performed? Describe how the frequency of checkpoints affects:

• System performance when no failure occurs
• The time it takes to recover from a system crash
• The time it takes to recover from a disk crash

Answer: A checkpoint log record indicates that a log record and its modified data has been written to stable storage and that the transaction need not to be redone in case of a system crash. Obviously, the more often checkpoints are performed, the less likely it is that redundant updates will have to be performed during the recovery process.
• System performance when no failure occurs—If no failures occur, the system must incur the cost of performing checkpoints that are essentially unnecessary. In this situation, performing checkpoints less often will lead to better system performance.
• The time it takes to recover from a system crash—The existence of a checkpoint record means that an operation will not have to be redone during system recovery. In this situation, the more often checkpoints were performed, the faster the recovery time is from a system crash.
• The time it takes to recover from a disk crash—The existence of a checkpoint record means that an operation will not have to be redone during system recovery. In this situation, the more often checkpoints were performed, the faster the recovery time is from a disk crash.