Here is the documentation for it..
SHMVIRT_ALLOCSEG and Memory Utilization
- A threshold at which the database server should allocate memory
- The alarm event security-code that is activated if the server cannot allocate the new memory segment.
- 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.
The SHMVIRT_ALLOCSEG configuration parameter specifies:
SHMVIRT_ALLOCSEG ensures that the server never runs out of memory.When you set this configuration parameter, you must:
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.