How to increase usable address space for 9.2 Oracle on RHEL4

Question

9.2 (on RHEL4):
The customer is using huge pages and also used VLM until switching the CPUs from Dual-Core to Quad-Core architecture
In his research he has found the following supported procedures:
- 10gR2 has already increased SGA limit for 32bit Linux 3,42 GB without VLM option.
- 10gR1 has an option to increase it by changing the address space and relinking the libraries.
- 9iR2 has the same option. But all that i have found in Metalink/Google is for RHEL 2.1 release.
The customer has removed VLM and now has the SGA within 32-bit Linux limit for 9i - 2.7 GB. They are considering moving to 64-bit architecture, but before that they are looking for a way to achieve in 9.2 the increasing of the SGA on RHEL4.
They are looking for a similar procedure as the one described in 200266.1. In this note they only mention RHEL 2.1. Is there a supported way to do this on RHEL 4 release?

Answer 1

There are all kinds of optimisations listed here, which are not all directly related to each other:
-Huge Pages: huge pages is the page size of the memory allocation done on the operating system layer. the reason for using hugepages is because the PTE table decreases because the number of PTE entries decreases when the size is larger.
-VLM: vlm is actually an oracle naming of using PAE, physical address extention. Using PAE means using addressable space beyond the normal 32-bit addressing is used, which is usable because of a trick on the processor level.
-switching from dual core to quad core: this switching means the operating system sees more processors (which is also a trick, because the number of CPU's is not increases, only the number of core's on the processor), which means the system is most likely able to do more processing in the same time.
-using 3.42GB: this can mean two things
-a) it means the oracle executable base address is lowered (which is already done for 10g by default)
-b) the hugemem kernel is used which has a 4:4 kernel split, instead of a 3:1 kernel split.
so the real question is: what is it you are looking for to use this? and are you sure you achieve that by increasing the SGA?
to be able to help your customer, please diagnose what you want to achieve, instead of just apply all kinds of technique which seem to be doing something with performance.