Set the SHMVIRTSIZE Configuration Parameter

Set the Virtual Shared-Memory Segment Size with the SHMVIRTSIZE Configuration Parameter

The SHMVIRTSIZE configuration parameter specifies the initial size of a virtual shared-memory segment. A suggested initial value is:

32000 + expected number of users * 800  

The best practice is to allocate only memory that is necessary for your environment. Therefore, you need to find the point at which, during the peak resource usage, IDS will not add any segments, while if you reduce the size of SHMVIRTSIZE, IDS will add another segment. The following method is one approach to find the value of SHMVIRTSIZE:

1. Set SHMVIRTSIZE to 50% of your memory.
2. During the peak resource usage, check how many additional segments have been added. You can use the onstat -g seg command. If no additional segments were added, then reduce the SHMVIRTSIZE. When you notice additional segments, proceed to the next step.
3. Use the following formula:

   new_SHMVIRTSIZE= old_SHMVIRTSIZE + (number_of_segments_added * SHMADD) 

4. When you find the optimal SHMVIRTSIZE, reduce the size a little to see if an additional segment is created. This is a way to verify your calculations.