shared memory - Mailing list pgsql-general

Hi y'all,
Here is the latest update.

The problem is with PostgreSQL allocating shared memory in BSD/OS 3.0.
The system has 128M of RAM and 262M of swap.
Currently postgres starts as:

su -l postgres -c '/usr/local/pgsql/bin/postmaster -i -d 3 -B 887 -o "-eF
-S 1024" >> /var/log/postgres 2>&1 &'

without problems. However, try to start with -B 1024 (which allocates 1024
of 8K blocks used for shared memory buffers)
and the following is logged:

FindExec: found "/usr/local/pgsql/bin/postgres" using argv[0]
binding ShmemCreate(key=52e2c1, size=8852184)
IpcMemoryCreate: shmget failed (Invalid argument) key=5432001, size=8852184,
per
mission=600
FATAL 1:  ShmemCreate: cannot create region
proc_exit(0) [#0]
shmem_exit(0) [#0]
exit(0)

OK, so we have to get BSD/OS to allocate more shared memory.

Note that the actual postgres error is related to calloc and malloc and
something else that specifically tells me to increase -B.
When -B is increased to 1024 the daemon dies as soon as it starts. The error
is not with memory usage but with memory allocation.

In this case setting

#options                        SYSVSHM
#options                        SYSVSEM
#options                        SYSVMSG

have no value. In some older version of BSD these would tell the compiler to
include the optional shared memory header files which are automatically
included in this version of BSD so these configs are redundant.

In previous attempts I have mucked with:
#options        "KMEMSIZE=\(16*1024*1024\)"
#options        "DFLDSIZ=\(32*1024*1024\)"
#options        "DFLSSIZ=\(4*1024*1024\)"
#options        "SOMAXCONN=128"
#options                "MAXDSIZ=\(256*1024*1024\)"
and made them available to the shell with ulimit. All to no avail.
Currently I use the default values from BSD so my front end processes get:
moe:~ $ ulimit -a
core file size (blocks)  unlimited
data seg size (kbytes)   32768
file size (blocks)       unlimited
max memory size (kbytes) 126280
stack size (kbytes)      32768
cpu time (seconds)       unlimited
max user processes       64
pipe size (512 bytes)    2
open files               128
virtual memory (kbytes)  65536

The backend of PostgreSQL is booted from a script /etc/rc.postgres with
ulimit -d unlimited just before the daemon is started so I am assuming that
postgres gets lots of data space.
(In fact I have checked this out and it is true).

Adjusting
#options                                "SHMMAXPGS=4096"
has no effect. The BSD default seems to be 2048 pages and pages are 4K.
That means the BSD default is around 8M which is just above my -B 886 (*8 =
7.5M) allocation for shared memory.
Allowing the system to soak up some shared mem for whatever reason I would
say this is the variable that I have to adjust.
So why doesn't it adjust!!??
Sin'ichiro M from sdi-users suggested it might be related to semaphore
identifiers:
but when I used a config from Daniel Kalchev
options         "KMAPENTRIES=4000" #prevents kmem malloc errors
options                 "SHMMAXPGS=32768"
options                 "SHMMNI=400"
options                 "SHMSEG=204"
options                 "SEMMNS=600"
Nothing different happens.

Finally there is a tip from Bruce that I need to increase SYSPTSIZE, the
number of dynamically allocated page tables for the kernel.
SYSPTSIZE is discovered by
bpatch -r sysptsize
In my case 28.
You can adjust this directly into the finished kernel by
bpatch sysptsize 40
Don't forget to reboot so that the change becomes effective.
This should actually allow me to allocate 12*4 = 48 extra Megs of shared
memory.
Guess what, no difference.

Thanks to anyone who has read this far.
Here are some questions:
1) What part of memory do shared memory buffers get loaded into: kernel?
data? This is to determine which of the ulimitable variables to concentrate
on.
2) Is it universally agreed that SHMMAXPGS is the key variable to address
and we just need to figure out what is related directly to it?
3) I don't have a clue - do you?
Best,
John Henderson