Thus spake Ricardo Ryoiti Sugawara Junior
>     Hi,
> 
>     Sometime ago I posted a message here asking for help as I was having
> trouble compiling postgresql on netbsd 1.5. I tried to force 100
> backends but I got that error:
> 
> ---
> IpcSemaphoreCreate: semget failed (No space left on device) key=5432017,
> num=16, permission=600
> This type of error is usually caused by an improper
> shared memory or System V IPC semaphore configuration.
> For more information, see the FAQ and platform-specific
> FAQ's in the source directory pgsql/doc or on our
> web site at http://www.postgresql.org.
> FATAL 1:  InitProcGlobal: IpcSemaphoreCreate failed
> ---
> 
>     Then I compiled it successfully with it's default value (32), but
> now I have to increase the number of backends. When I used -B 200 -N 100
> as parameters, this message is returned again.
>     I was looking for support on netbsd's documentation but there's (at
> least I didn't find) nothing. Postgresql's documentation says I have to
> increate the number of semaphores in the kernel, but there's no "number
> of semaphores" cfg option.

There is but it isn't documented.  Try something like this in your kernel
config file.

options     SHMMAXPGS=8192  # 1024 pages is the default
options     SEMMNI=64
options     SEMMNS=256

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