Performance Tuning - Question 030

Buffer cache performance is measured by selecting and comparing what information from which dynamic performance views?

A. Physical and logical reads from V$SYSSTAT

B . Logical and consistent reads from V$SYSSTAT

C . Physical and logical reads from V$BUFFER_POOL

D . Consistent gets and logical reads from V$BUFFER_POOL

Explanation:

Answer A: The formula is: 1-((physical reads - physical reads direct - physical reads direct (lob))/session logical reads); ). Eeach of these values is obtained from the VALUE column of V$SYSSTAT. We are measuring the hit ratio as the ratio of logical to physical reads. Logical reads are on a buffer cache block. Physical reads, of course, result in an I/O operation against a disk device. The V$BUFFER_POOL view is legitimate, but consistent gets, logical reads, and physical reads are not accumulated in this view.