Maximum shared-memory segment size
When the database server creates the required shared-memory segments, it attempts to acquire as large an operating-system segment as possible.
The database server receives an error from the operating system if the requested segment size exceeds the maximum size allowed. If the database server receives an error, it divides the requested size by two and tries again. Attempts at acquisition continue until the largest segment size that is a multiple of 8 KB can be created. Then the database server creates as many additional segments as it requires.