What is loading my server so much?

[Laszlo Nagy]

> 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?

Thanks

    Laszlo