Oracle OCP 19c 认证1Z0-083考试(96-100题) #已上传

While backing up to the Oracle Fast Recovery Area (FRA), you determined the backup is taking too long and suspect a performance bottleneck.

Which three are true about diagnosing and tuning these problems? (Choose three.)

A.    If an RMAN BACKUP VALIDATE command takes roughly the same time as an actual backup, then both read and write I/O are likely bottlenecks.

B.    Setting DBWR_IO_SLAVES to a non zero value can improve backup performance when using synchronous I/O.

C.    If an RMAN BACKUP VALIDATE command takes noticeably less than an actual backup, then write I/O is a likely bottleneck.

D.    If an RMAN BACKUP VALIDATE command takes roughly the same time as an actual backup, then read I/O is a likely bottleneck.

E.    Data files with a high value in V$BACKUP_SYNC_IO.DISCRETE_BYTES_PER_SECOND are a potential performance bottleneck when synchronous I/O is used.

F.    Setting DBWR_IO_SLAVES to a non zero value can improve backup performance when using asynchronous I/O/
 
G.    Data files with a high value in V$BACKUP_ASYNC_IO.SHORT_WAITS are a potential performance bottleneck when asynchronous I/O is used.

Answer: BCE

(解析:这道题考的东西多而深。)

确定磁带流或磁盘 I/O 是给定备份作业的瓶颈的一种可靠方法是比较运行备份任务所需的时间与运行相同任务的备份验证所需的时间。备份到磁带的备份验证执行与实际备份相同的磁盘读取,但不执行磁带    I/O。如果备份验证到磁带所需的时间明显少于实际备份到磁带所需的时间,则写入磁带可能是瓶颈。

使用同步 I/O,很难确定特定的瓶颈,因为所有同步 I/O 都是流程的瓶颈。调整同步 I/O 的 唯一方法是将速率(以字节/秒为单位)与设备的最大吞吐量进行比较。如果速率低于设备 指定的速率,则考虑调整备份和还原过程的这一方面。V$BACKUP_SYNC_IO    视图中的“DISCRETE_BYTES_PER_SECOND”列显示 I/O 速率。如果您在 V$BACKUP_SYNC_IO 中看到数 据,那么问题是您没有启用异步 I/O,或者您没有使用磁盘 I/O 从属设备。所以 E 答案是错 的。

如果您有同步 I/O,但您设置了 DBWR_IO_SLAVES 设备,则