15.3. Increasing Space for the SGA in Red Hat Enterprise Linux 2.1

To increase the maximum default size of shared memory for the SGA from 1.7 GB to 2.7GB, the Mapped Base Address (mapped_base) for shared libraries must be lowered from 0x40000000 (1 GB) to 0x10000000 (0.25 GB) and the SGA Attach Address for shared memory segments must be lowered from 0x50000000 (1.25 GB) to 0x15000000 (336 MB). Lowering the SGA attach address increases the available space for shared memory almost 1 GB. If shared memory starts at 0x15000000 (336 MB), then the space between 0x15000000 (336 MB) and 0xc0000000 (3GB) minus stack size becomes available for the SGA. Note the mapped base for shared libraries should 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.