Advisors are powerful tools for database management. They provide specific advice
on how to address key management challenges, covering a wide range of areas
including space, performance, and undo management. In general, advisors produce
more comprehensive recommendations than alerts. This is because alert generation is
intended to be low cost and have minimal impact on performance, whereas advisors
consume more resources and perform more detailed analysis. This, along with the
what-if capability of some advisors, provides vital information for tuning that cannot
be procured from any other source. Some advisors are run automatically.
Advisors are provided to help you improve database performance. These advisors
include Automatic Database Diagnostic Monitor (ADDM), SQL advisors, and memory
advisors. For example, the SGA Advisor graphically displays the impact on
performance of changing the size of the System Global Area (SGA).
You can run a performance advisor when faced with the following situations:
■ You want to resolve a problem in a specific area, for example, to determine why a
given SQL statement is consuming 50 percent of CPU time and what to do to
reduce its resource consumption.You can use the SQL Tuning Advisor.
■ You are planning to add memory to your system. You can use the Memory
Advisor to determine the database performance impact of increasing your SGA or
PGA (Program Global Area).
You can also invoke some of the advisors from the Performance Hub page, or through
recommendations from ADDM.
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