Max number of shared memory segment attached in parallel

ITEM: RTA000079058

Our Solution Centre is porting an application from an HP/UX                     
to Aix.                                                                         
Some processes need to attach a relevant number of shared                       
memory segment.                                                                 
When we try to ATTACH the 11th segment, no matter how many                      
shget() function has been called, we get an error                               
saying the maximum number of segments has been exceeded.                        
The third part that has written the code pretends to have                       
encountered the same problem with the HP platform too, and                      
that has been fixed by modifying a kernel parameter in a                        
master file.                                                                    
We did not find any way to customize this parameter                             
under AIX because it depends on some kind of addressing                         
limitation.                                                                     
Do you have any idea on how to bypass the problem                              
without introducing too changes in the code (mmap) ?                            
Do you think mmap decreases performances                                        
(customer is sensitive to performance items) ?                                  
                                                                                
ANSWER                                                                          
   You are correct, the limit is 10 shared memory segments.                     
   This parameter is not tuneable in AIX.  The suggested                        
   work around is to use the mmap().  I did not find a comparison               
   between the shared memory segments and mmap routines.                        
   Although it has been reported that the mmap implementation                   
   may cause more more page faults in the contention for the                    
   resources.                                                                   
                                                                                
S e a r c h - k e y w o r d s:                                                  
MMAP AND SHARED MEMORY.                                                        



WWQA: ITEM: RTA000079058 ITEM: RTA000079058

Dated: 02/1995 Category: ITSAI6000GE

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