Lots of RAM, how to use it?

Question

Hello everyone
Does anyone have any experience of running two instances from the same SAP system on a single Linux server in order to make use of a lot of available RAM? The situation is as follows:
- SAP R/3 4.6C, Oracle DB on 64-bit proprietary UNIX
- 3 app servers on 32-bit Intel processors running SLES 9, with 12GB of RAM each
- 3 small SAP instances with approximately 20 work processes each
- Each instance uses standard zero administration memory management (EM of 500MB, etc.) in order to make best use of shared memory, given the 32-bit address space limitations.
The SAP app instances don't use a lot of the underlying available memory so we see a free memory value of ~ 6GB on each server. What is the best way to make use of these unused memory resources? This is what I can think of:
1. increase the number of work processes on the already existing instances. Since Linux uses late swap allocation any additional memory load from additional WPs will tend to consume physical memory rather than swap space.
2. install a second SAP instance on each app server to make use of the available memory.
The main issue I can think of with the latter option is that it duplicates buffers, which is a waste but it also lessens the load on the existing buffers which are limited in size due to a 32-bit address space. Does anyone have a different idea to add to the list?
Thanks for your input,
Dáithí

Answer 1

In the case of having extra RAM, to get better performance is suggested to install more Dialog instances, or Apps instances for the production instance or the slowest instance.