calculate % of response time components

Hello Gurus,

In metalink note : 223117.1 - Tuning I/O related waits, I extracted the following, but, I couldn't understand the calculation made to get the % result. The extract of the note are as follows:

                                                                            
 Top 5 Wait Events                                                          
                                                                            
                                                                            
 ~~~~~~~~~~~~~~~~~                                                          
 Wait     % Total                                                           
                                                                            
                                                                            
 Event                                                                      
 Waits  Time (cs)   Wt                                                      
 Time                                                                       
                                                                            
                                                                            
 ------------------------                                                   
 --------------------                                                       
 ------------                                                               
 ------------ -------                                                       
                                                                            
                                                                            
 direct path read                                                           
 4,232       10,827                                                         
 52.01                                                                      
                                                                            
                                                                            
 db file scattered read                                                     
 6,105        6,264                                                         
 30.09                                                                      
                                                                            
                                                                            
 direct path write                                                          
 1,992        3,268                                                         
 15.70                                                                      
                                                                            
                                                                            
 control file parallel                                                      
 write                                                                      
 893          198     .95                                                   
                                                                            
                                                                            
 db file parallel write                                                     
 40          131     .63                                                    
                                                                            
                                                                            
                                                                            
 ------------------------                                                   
 ------------------------                                                   
 -------------                                                              
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 Based on this listing we                                                   
 may be tempted to                                                          
 immediately start                                                          
 looking at the                                                             
                                                                            
                                                                            
 causes between the                                                         


 'direct path read' and                                                     

 'db file scattered read'                                                   

 waits and                                                                  
                                                                            
                                                                            
 to try to tune them.                                                       
 This approach would not                                                    
 take into account                                                          


 'Service Time'.                                                            

                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 Here is the statistic                                                      
 that measures 'Service                                                     
 Time' from the same                                                        
 report:                                                                    
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 Statistic                                                                  
 Total   per Second                                                         
 per Trans                                                                  
                                                                            
                                                                            
 ------------------------                                                   
 ---------                                                                  
 ----------------                                                           
 ------------                                                               
 ------------                                                               
                                                                            
                                                                            
 CPU used by this session                                                   
 358,806        130.5                                                       
 12,372.6                                                                   
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 Let's do some simple                                                       
 math from these figures:                                                   
                                                                            
                                                                            


 'Wait Time' = 10,827 x                                                     

 100% / 52,01% = 20,817                                                     
 cs                                                                         
                                                                            
                                                                            


 'Service Time' = 358,806                                                   

 cs                                                                         
                                                                            
                                                                            


 'Response Time' =                                                          

 358,806 + 20,817 =                                                         
 379,623 cs                                                                 
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 If we now calculate                                                        
 percentages for all the                                                    


 'Response Time'                                                            

 components:                                                                
                                                                            
                                                                            
                                                                            
                                                                            
                                                                            
 CPU time                                                                   
 = 94.52%                                                                   
                                                                            
                                                                            
 direct path read                                                           
 =  2.85%                                                                   
                                                                            
                                                                            
 db file scattered read                                                     
 =  1.65%                                                                   
                                                                            
                                                                            
 direct path write                                                          
 =  0.86%                                                                   
                                                                            
                                                                            
 control file parallel                                                      
 write =  0.05%                                                             
                                                                            
                                                                            
 db file parallel write                                                     
 =  0.03%                                                                   
                                                                            

Could any one tell me, how the calculations are made to get the % of each wait event in the above?

Best Regards,

Syed Jaffar Hussain
OCP, DBA Consultant
ITD/Systems Department/Database Section
Tel : 01 4042222 x 1020
Mobile : 0506446723
Visit us on www.alfransi.com.sa
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