HOW CAN I FIND OUT WHY MY APPLICATION IS DOING

ITEM: RTA000050711

QUESTION:                                                                       
We have an application that when it runs seems to high number of                
context switches associated with it.  Normally the system runs at about         
average 40-50 context switches, but when this application runs we               
see 400-500 context switches.  The users say when this occurs the               
response time is increased tremendously.  This seems to make sense              
since context switches to take up time.  How can I measure why this             
context switching is taking place at such a high rate?  What tools can          
I use to look at this?  Does this seem like a high number?  The                 
application is a batch oriented update facility to a relational DB.             
                                                                                
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A: Four to Five Hundred context switches per second is a high number but        
   not extremely unusual.  If you are getting this many context switches,       
   is usually indicates that your processes are regularly getting blocked      
   waiting for file I/O, semaphores, etc.                                       
                                                                                
   The best tool you have available to track down the cause of this             
   'blockage' is the 'trace' command.  This command is fully documented         
   in the 'AIX Versions 3.2 and 4.1 Performance Tuning Guide' (SC23-2365)       
   and in InfoExplorer.                                                         
                                                                                
   This command allows you to watch for particular 'trace hooks'.  The          
   'dispatch' (106) and 'resume' (200) hooks should be of special               
   interest as these are the ones directly associated with context              
   switches.  You can see what system calls are made immediately before         
   these calls to determine the cause of the process becoming blocked.          
                                                                                
                                                                                
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This item was created from library item Q674123      FDRVF                      
                                                                                
Additional search words:                                                        
APPLIC APPLICATION CONTEXT DEC94 DOING FDRVF FIND IX LOCATE MEASURE             
OP OZNEW PERFORMANCE RISCPERF RISCSYSTEM SEARCH SOFTWARE SWITCHES               
SYS TUNE                                                                        
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                               



WWQA: ITEM: RTA000050711 ITEM: RTA000050711

Dated: 03/1996 Category: RISCPERF

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