Re: How to shoot yourself in the foot: kill -9 postmaster

* Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> [010306 10:35] wrote:
> Alfred Perlstein <bright(at)wintelcom(dot)net> writes:
>
> > What about encoding the shm id in the pidfile? Then one can just ask
> > how many processes are attached to that segment? (if it doesn't
> > exist, one can assume all backends have exited)
>
> Hmm ... that might actually be a pretty good idea. A small problem is
> that the shm key isn't yet selected at the time we initially create the
> lockfile, but I can't think of any reason that we could not go back and
> append the key to the lockfile afterwards.
>
> > you want the field 'shm_nattch'
>
> Are there any portability problems with relying on shm_nattch to be
> available? If not, I like this a lot...

Well it's available on FreeBSD and Solaris, I'm sure Redhat has
some deamon that resets the value to 0 periodically just for kicks
so it might not be viable... :)

Seriously, there's some dispute on the type that 'shm_nattch' is,
under Solaris it's "shmatt_t" (unsigned long afaik), under FreeBSD
it's 'short' (i should fix this. :)).

But since you're really only testing for 0'ness then it shouldn't
really be a problem.

--
-Alfred Perlstein - [bright(at)wintelcom(dot)net|alfred(at)freebsd(dot)org]