Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1, Tuning Manual

Page: 57 / 160

Lowering the Mapped Base Address for Shared Libraries in Red Hat Enterprise Linux 2.1
51
not be above the SGA attach address, example, between
0x15000000
(336 MB) and
0xc0000000
(3GB).
To increase the space for shared memory in Red Hat Enterprise Linux 2.1, the mapped base for
shared libraries for the Oracle processes must be changed by root. And the oracle user must relink
Oracle to relocate or lower the SGA attach address for shared memory segments.
15.4. Lowering the Mapped Base Address for Shared
Libraries in Red Hat Enterprise Linux 2.1
The default mapped base address for shared libraries in Red Hat Enterprise Linux 2.1 is
0x40000000
(1 GB). To lower the mapped base for a Linux process, the file
/proc/<pid>/mapped_base
must be
changed where
<pid>
stands for the process ID. This means that his is not a system wide parameter.
In order to change the mapped base for Oracle processes, the address mapping of the parent shell
terminal session that spawns Oracle processes (instance) must be changed for the child processes to
inherit the new mapping.
Login as oracle and run the following command to obtain the process ID of the shell where
sqlplus
will later be executed:
$ echo $$
Login as root in another shell terminal session and change the mapped_base for this process ID to
0x10000000
(decimal 268435456):
# echo 268435456 > /proc/<pid>/mapped_base
Now when Oracle processes are started with
sqlplus
in this shell, they will inherit the new mapping.
But before Oracle can be started, the SGA Attach Address for shared memory must be lowered as
well.
15.5. Lowering the SGA Attach Address for Shared Memory
Segments in Oracle 9i
The default SGA attach address for shared memory segments in Oracle 9i on Red Hat Enterprise
Linux 2.1 is 0x50000000 (1.25 GB). To lower the SGA attach address for shared memory, the Oracle
utility genksms must be used before the relinking:
Note
The examples below use # to represent comments not a root shell.
Login as oracle and execute the following commands:
# shutdown Oracle
SQL> shutdown
cd $ORACLE_HOME/rdbms/lib
# Make a backup of the ksms.s file if it exists