Oracle Instance tuning

http://docs.oracle.com/cd/E11882_01/server.112/e16638/instance_tune.htm

These are the main steps in the Oracle performance method for instance tuning:

1. Define the Problem
   Get candid feedback from users about the scope of the performance problem.
   
2. Examine the Host System and Examine the Oracle Database Statistics
   
   • After obtaining a full set of operating system, database, and application statistics, examine the data for any evidence of performance problems.
     
   • Consider the list of common performance errors to see whether the data gathered suggests that they are contributing to the problem.
     
   • Build a conceptual model of what is happening on the system using the performance data gathered.
     
3. Implement and Measure Change
   Propose changes to be made and the expected result of implementing the changes. Then, implement the changes and measure application performance.
   
4. Determine whether the performance objective defined in step 1 has been met. If not, then repeat steps 2 and 3 until the performance goals are met.
   
   Define the Problem
   
   Gather the following data:
   
   
   1. Identify the performance objective - What is the measure of acceptable performance? How many transactions an hour, or seconds, response time will meet the required performance level?
   2. Identify the scope of the problem - What is affected by the slowdown? For example, is the whole instance slow? Is it a particular application, program, specific operation, or a single user?
      
   3. Identify the time frame when the problem occurs - Is the problem only evident during peak hours? Does performance deteriorate over the course of the day? Was the slowdown gradual (over the space of months or weeks) or sudden?
      
   4. Quantify the slowdown - This helps identify the extent of the problem and also acts as a measure for comparison when deciding whether changes implemented to fix the problem have actually made an improvement. Find a consistently reproducible measure of the response time or job run time. How much worse are the timings than when the program was running well?
      
   5. Identify any changes - Identify what has changed since performance was acceptable. This may narrow the potential cause quickly. For example, has the operating system software, hardware, application software, or Oracle Database release been upgraded? Has more data been loaded into the system, or has the data volume or user population grown?