16.3. Oracle 10g SGA Sizes in Red Hat Enterprise Linux 3, 4 or 5
The following table shows how large the Oracle 10g SGA can be configured in Red Hat Enterprise Linux 3, 4 or 5 without using a shared memory file system. Shared memory file systems for the SGA are covered at Section 14.8, “Huge Pages and Shared Memory File System in Red Hat Enterprise Linux 3”Configuring Very Large Memory (VLM).
Table 16.1. Table showing how large SGA can be configured in Red Hat Enterprise Linux
|Red Hat Enterprise Kernel Type||10g Database Version||Default Supported SGA without VLM||Max Supported SGA without VLM||Comments|
|smp kernel (x86)||10g Release 1||Up to 1.7 GB||Up to 2.7 GB||10g R1 must be relinked to increase the SGA size to approx 2.7 GB|
|hugemem kernel (x86)||10g Release 1||Up to 2.7 GB||Up to 3.42 GB||10g R1 must be relinked to increase the SGA size to approx 3.42 GB|
|smp kernel (x86)||10g Release 2||Up to ~2.2 GB (*)||Up to ~2.2 GB (*)||No relink of 10g R2 is necessary but the SGA Attach Address is a little bit higher than in R1|
|hugemem kernel (x86)||10g Release 2||Up to ~3.3 GB (*)||Up to ~3.3 GB (*)||No relink of 10g R2 is necessary but the SGA Attach Address is a little bit higher than in R1|
(*) When performing test scenarios with 10g R2 the database was not able to start up if sga_target was larger than 2350000000 bytes on a smp kernel, and if sga_target was larger than 3550000000 bytes on a hugemem kernel.
In Oracle 10g R2 the SGA size can be increased to approximately 2.7 GB using the smp kernel and to approximately 3.42 GB using the hugemem kernel. The SGA attach address does not have to be changed for that. To accommodate the same SGA sizes in Oracle 10g R1, the Section 16.4, “Lowering the SGA Attach Address in Oracle 10g” must be lowered.
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.