[DOCS] Issue with SHMALL parameter

[data tanger]

Hi,

I'm using postgresql 9.1 as my database server on a linux server that has 8 GB of RAM.

After I changed the shared_buffers parameter to 2GB, I get the following error when I try to start postgres:

FATAL:  could not create shared memory segment: Cannot allocate memory

DETAIL:  Failed system call was shmget(key=5432001, size=2221539328, 03600).

Here are the shmall and the shmax params of my server:

#cat /proc/sys/kernel/shmmax     

68719476736

#cat /proc/sys/kernel/shmall     

4294967296

So as you see, shmall is greater than the requested size by postgres. Anyone have and idea?

thank you

[Tom Lane]

data tanger <datat...@hotmail.fr> writes:
> Here are the shmall and the shmax params of my server:
> #cat /proc/sys/kernel/shmmax 68719476736
> #cat /proc/sys/kernel/shmall 4294967296

SHMALL is measured in pages not bytes on Linux. I wonder if that value
is too large and is causing an internal integer overflow in the kernel.

regards, tom lane


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[data tanger]

Thank you for your answer. I think the value of shmall I have is very common cause I've seen it many times in other servers.

Do you think there maybe a link between the request size of postgres and the swap size?

Here is the output of free -m

free -m

             total       used       free     shared    buffers     cached

Mem:          7867       1860       6007          0          5        595

-/+ buffers/cache:       1258       6609

Swap:         1023          2       1021

Regards,