Great. I have applied the following documentation patch for CVS HEAD
and 8.1.X.
It seems you are saying that shmmax and shmall must be multiples of 4k,
and I added that to the docs. It previously only mentioned shmmax in
that regard.
---------------------------------------------------------------------------
Chris Campbell wrote:
> The definitive answer can be found in the source code for the Darwin
> kernel, xnu (links are below):
>
> 1. The shmmax, shmmin, shmmni, shmseg, and shmall settings cannot be
> changed after the shared memory system is initialized
>
> 2. The shared memory system is initialized immediately after all 5
> settings have been configured
>
> 3. The shmall setting must be a multiple of the page size (on both
> 10.3 and 10.4)
>
> Here are excerpts from the sysctl_shminfo() function found in
> sysv_shm.c:
>
> [1]
> /* Set the values only if shared memory is not initialised */
> if (!shm_inited) {
> if ((error = SYSCTL_IN(req, arg1, sizeof(user_ssize_t)))
> != 0) {
> sysctl_shminfo_ret = error;
> goto sysctl_shminfo_out;
> }
>
> [2]
> /* Initialize only when all values are set */
> if ((shminfo.shmmax != (user_ssize_t)-1) &&
> (shminfo.shmmin != (user_ssize_t)-1) &&
> (shminfo.shmmni != (user_ssize_t)-1) &&
> (shminfo.shmseg != (user_ssize_t)-1) &&
> (shminfo.shmall != (user_ssize_t)-1)) {
> shminit(NULL);
> }
>
>
> [3]
> (10.3)
> if (arg1 == &shminfo.shmmax) {
> if (shminfo.shmmax & PAGE_MASK) {
> shminfo.shmmax = -1;
> return(EINVAL);
> }
> }
>
> (10.4)
> if (arg1 == &shminfo.shmmax) {
> if (shminfo.shmmax & PAGE_MASK_64) {
> shminfo.shmmax = -1;
> return(EINVAL);
> }
> }
>
> PAGE_MASK is "(PAGE_SIZE - 1)", and PAGE_MASK_64 is simply "(unsigned
> long long)PAGE_MASK"
>
>
> /etc/rc contains commands to set all 5 of the parameters. In 10.3.9
> and later, you can place your own customized settings inside /etc/
> sysctl.conf that will be executed before /etc/rc's commands. But if
> you don't set them all, the shared memory system isn't initialized,
> and /etc/rc will overwrite them.
>
> Does that make sense?
>
> In a nutshell, if you want to customize the shared memory settings,
> you must:
>
> (On 10.3.9 and later)
> Set ALL 5 settings inside /etc/sysctl.conf, and make sure that shmmax
> is a multiple of the page size (4096?). The page size is a runtime
> variable that's set by kernel bootstrap mechanisms calling
> vm_set_page_size() (I haven't tracked those down yet).
>
> (On earlier systems)
> Modify the desired settings inside /etc/rc, and be aware that OS
> updates will overwrite your changes. If you upgrade to 10.3.9,
> migrate to using /etc/sysctl.conf.
>
> In my own OS X products that use a PostgreSQL server, I install an /
> etc/sysctl.conf file on all servers. If installing on anything
> earlier than 10.3, my installer modifies /etc/rc. That way, when the
> customer upgrades their server to 10.3.9 and the /etc/rc file is
> overwritten, the /etc/sysctl.conf file is already in place.
>
> Thanks!
>
> - Chris
>
>
> Referenced source code:
>
> Mac OS X 10.4.4:
> http://www.opensource.apple.com/darwinsource/10.4.4.ppc/
> xnu-792.6.56/bsd/kern/sysv_shm.c
>
> Mac OS X 10.3.9:
> http://www.opensource.apple.com/darwinsource/10.3.9/xnu-517.12.7/
> bsd/kern/sysv_shm.c
>
> Mac OS X 10.3:
> http://www.opensource.apple.com/darwinsource/10.3/xnu-517/bsd/
> kern/sysv_shm.c
>
--
Bruce Momjian http://candle.pha.pa.us
SRA OSS, Inc. http://www.sraoss.com
+ If your life is a hard drive, Christ can be your backup. +
Index: doc/src/sgml/runtime.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v
retrieving revision 1.361
diff -c -c -r1.361 runtime.sgml
*** doc/src/sgml/runtime.sgml 5 Jan 2006 03:01:33 -0000 1.361
--- doc/src/sgml/runtime.sgml 2 Mar 2006 20:28:06 -0000
***************
*** 886,904 ****
changes take effect.
</para>
! <!--
! It might appear that we could recommend putting sysctl settings into
! /etc/sysctl.conf so that they aren't destroyed by OS version updates.
! This does not work as of OS X 10.4.2, however, because /etc/rc
! promptly overrides whatever SHM settings are read from sysctl.conf :-(
! Perhaps someday we can recommend this ...
! -->
<para>
! <varname>SHMALL</> is measured in 4KB pages on this platform.
! Also note that some releases of OS X will reject attempts to
! set <varname>SHMMAX</> to a value that isn't an exact multiple
! of 4096.
</para>
</listitem>
</varlistentry>
--- 886,904 ----
changes take effect.
</para>
! <para>
! In OS X 10.3.9 and later, the file <filename>/etc/sysctl.conf</>
! allows shared memory setting to be saved across operating system
! upgrades, and is the recommended method for setting these
! parameters. When using this file, all five shared memory values
! must be set or the changes will be ignored.
! </para>
<para>
! <varname>SHMALL</> is measured in 4KB pages on this platform,
! and recent releases of OS X reject attempts to set
! <varname>SHMALL</> and <varname>SHMMAX</> to a value
! that isn't an exact multiple of 4096.
</para>
</listitem>
</varlistentry>
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
