問題文
A new administrator asks what the repository actually stores when a snapshot is taken, and why two snapshots are needed before a report can be produced. Which explanation is correct?
選択肢
- A snapshot records the sampled sessions of the last hour so a report needs the earlier one to fill the gap between the samples.
- A snapshot records the counters and then resets them to zero so a report needs the earlier one only to know when the period began.
- A snapshot records the cumulative counters at one instant so a report has to subtract one set of counters from another to obtain the values for a period.
- A snapshot records a plan for each statement that ran so a report needs the earlier one to see which plan the optimizer had chosen before.