Database Reference
In-Depth Information
Checking kernel parameters
The Linux kernel has lots of tunables to affect the way it operates. The Oracle database makes intensive use of these,
and you need to modify the standard parameters before you can install the database or Grid Infrastructure software.
Many kernel parameters can be changed at runtime by echoing values to files in the /proc file system. To make these
changes permanent, you need to modify the /etc/sysctl.conf file which is parsed at every system boot.
Oracle made it somewhat easier by adding an option to the OUI interface allowing you to run a fixup script to
correct these values to their minimum required settings. If you are using Oracle Linux 5, you could alternatively install
the oracle-validated RPM which helps setting some of the parameters before the installation. There is a similar RPM
available for Oracle 12.1, named Oracle RDBMS Server 12cR1 Pre-Install RPM. You should also consult with your
system administration team to adjust the values to fit your hardware optimally.
Tables 5-3 and 5-4 list the parameters and provide advice on setting them. Table 5-3 focuses upon semaphore
parameters. Table 5-4 lists all the others. It makes sense to check the parameters even after having installed the
preinstall RPM!
Table 5-3. Kernel Parameters relating to semaphores
Kernel
parameter
Recommended
(minimum) value
Description
semmsl
250
The maximum number of semaphores in a semaphore set.
Applications always request semaphores in sets. The number
of sets available is defined by the semmni value, see below.
Each of these sets contains semmsl semaphores.
semmns
32000
The total number of semaphores permitted system-wide.
The value of 32000 = semmsl * semmni.
semopm
100
Sets a limit for the maximum number of operations in a single
semaphore-related operating system call.
semmni
128
The maximum number of semaphore sets.
Table 5-4. Other kernal parameters and their recommended minimums
Kernel
parameter
Recommended
(minimum) value
Description
shmmax
Half the physical memory;
set to 4398046511104 byte
by Oracle preinstall
Shared Memory Max (size) defines the maximum size of an
individual shared memory segment in bytes. When you start
an Oracle instance, it tries to allocate the SGA from shared
memory. If the total size of the SGA is greater than shmmax
then Oracle will create the SGA consisting of multiple smaller
segments, which can have implications on NUMA-enabled
systems since memory might not be node-local.
The Oracle validated RPM uses the maximum size
permissible on the 64bit platform: 4TB. That should be
enough to fit even the largest SGA!
( continued )
 
 
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