Re: postgres start problems with memory

On Thu, 30 Sep 2004 13:39:57 -0500, Josh Close <narshe@gmail.com> wrote:
> I keep getting this error.
>
> DETAIL:  Failed system call was shmget(key=5432001, size=34037760, 03600).
> HINT:  This error usually means that PostgreSQL's request for a shared
> memory segment exceeded your kernel's SHMMAX parameter.  You can
> either reduce the request size or reconfigure the kernel with larger
> SHMMAX.  To reduce the request size (currently 34037760 bytes), reduce
> PostgreSQL's shared_buffers parameter (currently 2048) and/or its
> max_connections parameter (currently 1024).
>         If the request size is already small, it's possible that it is
> less than your kernel's SHMMIN parameter, in which case raising the
> request size or reconfiguring SHMMIN is called for.
>         The PostgreSQL documentation contains more information about
> shared memory configuration.
>
> I've change kernel.shmmax and kernel.shmmin a couple of times, and I
> can't get it to work.
>
> I'm passing
>
> -N 1024
> -B 2048
>
> to postmaster, it's the gentoo install default. This is what I have
> right now for kernel values
>
> root # sysctl -a | grep shm
> kernel.shmmni = 4096
> kernel.shmall = 31584400
> kernel.shmmax = 31584400
>
> Does the amount of RAM in the computer make a difference? I added more
> RAM recently and upped the kernel to 4mb ram (something-or-rather) to
> allow for over 1gig. It started up fine then. I restarted the computer
> today and I can't get postgres to start now.
>
> How can I fix this? What are some good standards? I've read this
> http://www.postgresql.org/docs/7.4/interactive/kernel-resources.html
> but it didn't help much.
>
> Thanks.
>
> -Josh

Ok. I got it started by changing

kernel.shmmax = 134217728
kernel.shmall = 134217728

Why does this make it work? wasn't it high enough before? I went by
the "reasonable value" that the postgres docs says of

250 kB + 8.2 kB * shared_buffers + 14.2 kB * max_connections up to infinity

but that didn't work.

Can anyone explain this to me? I'd like to be able to customize
postgresql, and I'm getting 2 gigs of ram to put in.

Thanks.

-Josh