16.3. Oracle 10g SGA Sizes in Red Hat Enterprise Linux 3, 4 or 5

Lowering the SGA attach address in Oracle restricts the remaining 32 bit address space for Oracle processes. This means that less address space will be available for e.g. PGA memory. If the application uses a lot of PGA memory, then PGA allocations could fail even if there is sufficient free physical memory. Therefore, in certain cases it may be prudent not to change the SGA Attach Address to increase the SGA size but to use Chapter 17, Using Very Large Memory (VLM) instead. Also, if the SGA size is larger but less than 4GB to fit in memory address space, then the Chapter 17, Using Very Large Memory (VLM) solution should be considered first before switching to the hugemem kernel on a small system, unless the system has lots of physical memory. The hugemem kernel is not recommended on systems with less than 8GB of RAM due to some overhead issues in the kernel, see also Section 2.2, “32 bit Architecture and the hugemem Kernel”. If larger SGA sizes are needed than listed in the above table, then Chapter 17, Using Very Large Memory (VLM) must obviously be used on x86 platforms.