052-218(新增70题2018)
Because of a power outage, instance failure has occurred.
From what point in the redo log does recovery begin and where does it end?
A. current redo log and inactive redo log
B. checkpoint position to end of redo log
C. beginning of redo log to end of redo log
D. all redo logs before the point of last commit
E. beginning of redo log to checkpoint position
Answer: B
Instance recovery uses checkpoints to determine which changes must be applied to the data files. The checkpoint position guarantees that every committed change with an SCN lower than the checkpoint SCN is saved to the data files.
Figure 13-5 depicts the redo thread in the online redo log.
Figure 13-5 Checkpoint Position in Online Redo Log
During instance recovery, the database must apply the changes that occur between the checkpoint position and the end of the redo thread. As shown in Figure 13-5, some changes may already have been written to the data files. However, only changes with SCNs lower than the checkpoint position are guaranteed to be on disk.
