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<Chapter Id="runtime">

<row>

<entry><varname>SHMMAX</></>

<entry>Maximum size of shared memory segment (bytes)</>

<entry>512 kB + 8192 * buffers + extra ... infinity</entry>

<entry>700 kB + 8192 * buffers + extra ... infinity</entry>

</row>

<row>

<entry>1 (at most about 256 kB)</>

</row>

<row>

<entry><varname>SHMALL</></>

<entry>Total amount of shared memory available (bytes or pages)</>

<entry>if bytes, same as SHMMAX; if pages, ceil(SHMMAX/PAGE_SIZE)</>

</row>

<row>

<entry><varname>SHMSEG</></>

<entry>Maximum number of shared memory segments per process</>

<para>

By default, only 4 MB of shared memory is supported. Keep in

mind that shared memory is not pageable; it is locked in RAM.

The shared memory parameters are:

<programlisting>

#define SHMMAX/* max shared memory segment size (bytes) */

#define SHMMIN/* min shared memory segment size (bytes) */

#define SHMMNI/* max number of shared memory identifiers */

#define SHMSEG/* max shared memory segments per process */

#define SHMALL/* max amount of shared memory (pages) */

</programlisting>

To increase the number of buffers supported by the postmaster, add the

following to your kernel config file. A <varname>SHMALL</> value of 1024

represents 4MB of shared memory. Increase it accordingly:

To increase the number of shared buffers supported by the

postmaster, add the following to your kernel config file. A

<varname>SHMALL</> value of 1024 represents 4MB of shared

memory. The following increases the maximum shared memory area

to 32 MB:

<programlisting>

options "SHMALL=4096"

options "SHMALL=8192"

options "SHMMAX=\(SHMALL*PAGE_SIZE\)"

</programlisting>

</para>

</formalpara>

<para>

For those running 4.1 or later, justrecompile thekernel and

reboot. For those running earlier releases, use

<application>bpatch</> to find the <varname>sysptsize</> value

forthe current kernel. This is computed dynamically at

bootup.

For those running 4.1 or later, justmake theabove changes,

recompile the kernel, andreboot. For those running earlier

releases, use<application>bpatch</> to find the

<varname>sysptsize</> value inthe current kernel. This is

computed dynamically atbootup.

<screen>

$ <userinput>bpatch -r sysptsize</>

<computeroutput>0x9 = 9</>

</screen>

Next, change <varname>SYSPTSIZE</> to a hard-coded value. Use

the bpatch value, plus add 1 for every additional 4 MB of

Next, add <varname>SYSPTSIZE</> as a hard-coded value in the

kernel config file. Increase the value you found using

<application>bpatch</>. Add 1 for every additional 4 MB of

shared memory you desire.

<programlisting>

options "SYSPTSIZE=13"

options "SYSPTSIZE=16"

</programlisting>

<varname>sysptsize</> can not be changed by sysctl on the fly.

<varname>sysptsize</> can not be changed by sysctl.

</para>

<formalpara>

</para>

</formalpara>

<para>

The defaults are in <filename>/sys/sys/sem.h</>:

<programlisting>

#define SEMMNI 10 /* # of semaphore identifiers */

#define SEMMNS 60 /* # of semaphores in system */

#define SEMUME 10 /* max # of undo entries per process */

#define SEMMNU 30 /* # of undo structures in system */

</programlisting>

Set the values you want in your kernel config file, e.g.:

<programlisting>

options "SEMMNI=40"