The SHMVIRT_ALLOCSEG configuration parameter and memory utilization

The SHMVIRT_ALLOCSEG configuration parameter specifies a threshold at which the database server should allocate memory. This configuration parameter also defines an alarm event security-code that is activated if the server cannot allocate the new memory segment, thus ensuring that the database server never runs out of memory.

When you set the SHMVIRT_ALLOCSEG configuration parameter, you must:
  • Specify the percentage of memory used or the whole number of kilobytes remaining on the server. You cannot use negative values and values between 0 and .39.
  • Specify the alarm event-security code, which is a value ranging from 1 (not noteworthy) to 5 (fatal). If you do not specify an event-security code, the server sets the value to 3, which is the default value.
Example 1: 
SHMVIRT_ALLOCSEG 3000, 4
This specifies that if the database serve has 3000 kilobytes remaining in virtual memory and additional kilobytes of memory cannot be allocated, the server raises an alarm level of 4.
Example 2: 
SHMVIRT_ALLOCSEG .8, 4
This specifies that if the database server has twenty percent remaining in virtual memory and additional kilobytes of memory cannot be allocated, the server raises an alarm level of 4.