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To predict the percentage of reads saved for different database cache sizes:
1. In EM Express, from the Configuration menu, select Memory.
The Memory Management page appears. In the Memory Settings section, the
Management Mode value is Manual in the SGA Memory subsection.This
indicates that Manual Shared Memory Management is enabled for the database.
2. Use the Buffer Cache Advisor graph (which appears to the right of the Memory
Settings section) to predict the percentage of reads saved for potential database
cache sizes.
In the Buffer Cache Advisor graph:
■ Potential values for the DB_CACHE_SIZE initialization parameter (in MB) are
represented on the horizontal axis of the graph. The current setting of the DB_
CACHE_SIZE initialization parameter is indicated by a blue dot.
■ The corresponding values of reads saved are represented on the vertical axis
of the graph. The plotted values are expressed as a percentage relative to the
current setting of the DB_CACHE_SIZE initialization parameter.
Negative values represent the percentage of an increase in reads (when the
memory allotted to Oracle is smaller than the current setting), while positive
values represent the percentage of decrease in reads (when the memory
alloted to Oracle is larger than the current setting.
An orange line on the graph plots different values that can be specified for the DB_
CACHE_SIZE initialization parameter. Click any dot on the orange line to see a
prediction of the percentage of reads saved for the DB_CACHE_SIZE value
represented by that dot.
In this figure, the Buffer Cache Advisor graph indicates that increasing the current
value of the DB_CACHE_SIZE initialization parameter will not increase the
percentage of reads saved.
3. To change the value of the DB_CACHE_SIZE initialization parameter:
a. Click Configure Memory on the Memory Management page.
The Initialization Parameter page appears.
b. Select the DB_CACHE_SIZE initialization parameter and click Set.
The Set Initialization Parameter page appears.
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