System information

Tips and Techniques: Install and Configure Oracle9i on Red Hat Linux
Advanced Server
Shared memory file system on /dev/shm (shmfs):
To create large SGA size > 1.7 GB Shared memory file system (shmfs) is used.
Following commands could be used to create Shared memory file system (shmfs)
and these need to be added to /etc/rc.local. User could also create Shared memory
file system (shmfs) using /etc/fstab. It would be a good idea to remove or
comment out existing entry for /dev/shm from /etc/fstab before adding entry for
/dev/shm.
mount -t shm shmfs -o size=32g /dev/shm
(m and k also works fine) OR
mount -t shm shmfs -o nr_blocks=8388608 /dev/shm
Using Shared memory file system (shmfs) on 8 GB system, SGA of upto 7 GB
could be created. To take advantage of Shared memory file system (shmfs), the
following parameter needs to be set in init<sid>.ora
use_indirect_data_buffers=true
It has to be ensured that SHMMAX is set to a proper value, before increasing SGA
using Shared memory file system (shmfs) solution.
Lower mapped base:
Lowering mapped base helps increase SGA size from 1.7 GB to 2.7 GB without
using Shared memory file system (shmfs). This is true for any system with atleast
4GB of memory.
To lower mapped base, any of following techniques could be used.
The pid of the process (shell) that started oracle needs to be identified. This could
be done using ps command. The pid could also be identified using "echo $$". As
root, the following command is executed to lower mapped_base to 0x10000000.
echo 268435456 > /proc/$pid/mapped_base
where $pid is the pid of the shell from which Oracle was started.
Lowering mapped base works with both VLM and non-VLM installations. This
requires relinking of Oracle. To relink Oracle to make use of Lower mapped base,
the following commands need to be run from $ORACLE_HOME/rdbms/lib.
genksms -s 0x15000000 > ksms.s
make -f ins_rdbms.mk ksms.o
make -f ins_rdbms.mk ioracle
To take advantage of lower mapped base solution, proper value needs to be set for
SHMMAX, as described in the Shared memory section of this paper.
Tips and Techniques: Install and Configure Oracle9i on Red Hat Linux Advanced Server Page 13