Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1, Tuning Manual

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Lowering the SGA Attach Address in Oracle 10g
57
Red Hat
Enterprise
Kernel Type
10g Database
Version
Default
Supported SGA
without VLM
Max Supported
SGA without
VLM
Comments
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
Table 16.1. Table showing how large SGA can be configured in Red Hat Enterprise Linux
(*) 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.
Note
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.
16.4. Lowering the SGA Attach Address in Oracle 10g
Starting with Oracle 10g R2 the SGA attach address does not have to be lowered for creating larger
SGAs. However, Oracle 10g R1 must be relinked for larger SGAs.
The following commands were executed on a 10g R1 database system:
# ps -ef | grep "[o]ra_ckpt"
oracle 3035 1 0 23:21 ? 00:00:00 ora_ckpt_orcl