421.When tuning Automatic PGA Memory Management, which of the following views will provide the information specified?
A. The V$PGA_TARGET_ADVICE view shows the predicted cache hit-ratio improvement if you increase PGA_AGGREGATE_TARGET.
B. The V$PGA_TARGET_ADVICE view shows how the V$SQL_WORKAREA histogram will change if you change the value of PGA_AGGREGATE_TARGET.
C. The V$PGA_TARGET_ADVICE_HISTOGRAM view shows how the V$SQL_WORKAREA_HISTOGRAM will change if you switch between Manual and Automatic PGA Memory Management.
D. The V$PGA_TARGET_ADVICE view shows how performance will improve for the different work areas if you switch from Manual to Automatic PGA Memory Management.
Answer: A
答案解析：
V$PGA_TARGET_ADVICE predicts how the cache hit percentage and over allocation count statistics displayed by the V$PGASTAT performance view would
be impacted if the value of the PGA_AGGREGATE_TARGET parameter is changed. The prediction is performed for various values of the PGA_AGGREGATE_TARGET parameter,
selected around its current value. The advice statistic is generated by simulating the past workload run by the instance.
The content of the view is empty if PGA_AGGREGATE_TARGET is not set. In addition, the content of this view is not updated if the STATISTICS_LEVEL parameter is set to BASIC. Base statistics
for this view are reset at instance startup and when the value of the PGA_AGGREGATE_TARGET initialization parameter is dynamically modified.