Installation guide

on this system would be 1048576 KB (512*1024*2). If memlock is too small, then no single page will be allo-

cated when the Oracle database starts. For more information on setting shell limits, see Setting Shell Limits for

the Oracle User section of this document.

ing the database.

After an Oracle database startup, you can verify the usage of Huge Pages by verifying that the number of free

Huge Pages has decreased:

$ grep HugePages_Free /proc/meminfo

HugePages_Free: 0

To free the Huge Pages pool, execute:

# echo 0 > /proc/sys/vm/nr_hugepages

This command can take a while to finish.

Setting Shared Memory

Shared memory allows processes to access common structures and data by placing them in shared memory seg-

ments. It is the fastest form of Inter-process Communication (IPC) available since no kernel involvement occurs

when data is passed between the processes. In fact, data does not need to be copied between the processes.

Oracle uses shared memory segments for the SGA.

To see all shared memory settings, execute:

$ ipcs -lm

------ Shared Memory Limits --------

max number of segments = 4096

max seg size (kbytes) = 67108864

max total shared memory (kbytes) = 17179869184

min seg size (bytes) = 1

Setting SHMMAX Parameter

This parameter defines the maximum size in bytes of a single shared memory segment that a Linux process can

allocate in its virtual address space. On a 32-bit platform with 4+4GB split, such as Red Hat Enterprise Linux 4

with hugemem i686 kernel, the maximum size of shared memory segment used by Oracle 10g SGA is limited to

approximately 3.42 GB since virtual address space is also needed for other things such as shared libraries. Since

Red Hat Enterprise Linux 5 does not provide a 32-bit kernel with 4+4GB split,it is not recommended on the

x86 platform for Oracle database server use on systems with greater than 4GB of RAM. Use either Red Hat

Enterprise Linux 5 for x86_64 if the hardware can operate in 64-bit mode or Red Hat Enterprise Linux 4 for x86

with hugemem kernel on legacy 32-bit hardware.