What is loading my server so much?

[Bill Moran]

On Thu, 9 Dec 2010 19:30:08 -0600
Gary Gatten <Ggatten at waddell.com> wrote:

> Could there be a ulimit issue as well?

I think shared memory is unaffected by ulimits ... at least, I've never
had trouble with ulimit preventing PostgreSQL from allocating gigs and
gigs of shared memory, and I don't recall every having to bump ulimits.

> 
> ----- Original Message -----
> From: owner-freebsd-questions at freebsd.org <owner-freebsd-questions at freebsd.org>
> To: Laszlo Nagy <gandalf at shopzeus.com>
> Cc: questions at freebsd.org <questions at freebsd.org>; danieleff at gmail.com <danieleff at gmail.com>
> Sent: Thu Dec 09 18:55:26 2010
> Subject: Re: What is loading my server so much?
> 
> On Fri, 10 Dec 2010 00:15:14 +0100
> Laszlo Nagy <gandalf at shopzeus.com> wrote:
> 
> > 
> > > First off, you have 24G of RAM available and PostgreSQL only seems to
> > > have access to 400M of it.  Bump shared_buffers up to 2 or 3 G at least,
> > > and bump up work_mem to at least a few hundred meg, and
> > > maintenance_work_mem up to at 1/2G or so.
> > 
> > All right. Here is what I did. I setup a new shmmax value this way:
> > 
> > sysctl kern.ipc.shmmax=8589934592
> > 
> > It is 8G.  (By the way I also have kern.ipc.shm_use_phys: 1 ) Then I 
> > have changed shared_mem to 1024MB in postgresql.conf.
> > Then I tried to start postgresql I got this message in the log:
> > 
> > Dec  9 17:53:59 shopzeus postgres[27247]: [1-4]         The PostgreSQL 
> > documentation contains more information about shared memory configuration.
> > Dec  9 17:55:52 shopzeus postgres[27328]: [1-1] FATAL:  could not create 
> > shared memory segment: Cannot allocate memory
> > Dec  9 17:55:52 shopzeus postgres[27328]: [1-2] DETAIL:  Failed system 
> > call was shmget(key=5432001, size=1105051648, 03600).
> > Dec  9 17:55:52 shopzeus postgres[27328]: [1-3] HINT:  This error 
> > usually means that PostgreSQL's request for a shared memory segment 
> > exceeded available memory or swap space. To reduce the request size 
> > (currently 1105051648 bytes), reduce PostgreSQL's shared_buffers 
> > parameter (currently 131072) and/or its max_connections parameter 
> > (currently 203).
> > Dec  9 17:55:52 shopzeus postgres[27328]: [1-4]         The PostgreSQL 
> > documentation contains more information about shared memory configuration.
> > 
> > I do not understand.
> > 
> > Doc says these:
> > 
> > "max_connections cost ~ 400 bytes of shared memory slot, plus lock space 
> > (see max_locks_per_transaction)."
> > 
> > Even if I had max_connections = 5000, total shared memory required would 
> > be way below shmmax=8G.
> > 
> > What am I missing here?
> 
> Did you bump kern.ipc.shmall?  The one you bumped is the maximum size of
> a single shared memory request, shmall is the maximum amount of shared
> memory for the entire system.  They both have to be increased.  To make
> it more confusing, shmall is in pages, not bytes, so you have to divide
> by pagesize (sysctl hw.pagesize).
> 
> -Bill
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