Configuring the Dedicated Memory feature

Dedicated Memory is a configurable feature that can improve the performance of some software when running on advanced Intel processors: Pentium and Pentium Pro processors support this feature. If you configure dedicated memory on a processor that does not support this feature, it will have no effect. Dedicated Memory can improve performance of applications that create large shared memory segments using the shared memory primitives described in shmget(2), shmctl(2), and shmop(2).

The DEDICATED_MEMORY parameter specifies the size, in 4k pages, of memory which is to be reserved at startup time and dedicated for special purposes. Such purposes include shared memory segments which are 1MB or larger, shared memory segments which use fine-grained affinity (FGA shm), and dynamically mapped shared memory (dshm) segments. You must set DEDICATED_MEMORY in order to dedicate any amount of system memory.

To configure the Dedicated Memory feature:

1. Configure your system so that the pse driver is included in your system's operating system kernel. Edit the file /etc/conf/sdevice.d/pse so that the second field of the last line of the file is ``Y'' rather than ``N''.

2. If you have more than 4GB then you must use PAE mode. To use PAE mode, you must specify ENABLE_4GB_MEM=Y to the boot loader.

3. Set the parameter DEDICATED_MEMORY. You can then reconfigure the database and bring it up.

4. Optionally, set the parameter GENERAL_MEMORY to the amount of memory you want to reserve for general purpose use. This acts as a safety net which enables the system to boot and operate normally even if a bank of memory fails.

5. Run idbuild(1M) and then reboot the system to build and boot the reconfigured kernel.

Depending on the applications and workload involved, you might consider using UVIRT_EXTENSION as an alternative to DSHM.