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

* Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> [010306 11:30] wrote:
> Alfred Perlstein <bright(at)wintelcom(dot)net> writes:
> > * Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> [010306 11:03] wrote:
> >> I notice that our BeOS and QNX emulations of shmctl() don't support
> >> IPC_STAT, but that could be dealt with, at least to the extent of
> >> stubbing it out.
>
> > Well since we already have spinlocks, I can't see why we can't
> > keep the refcount and spinlock in a special place in the shm
> > for all cases?
>
> No, we mustn't go there. If the kernel isn't keeping the refcount
> then it's worse than useless: as soon as some process crashes without
> decrementing its refcount, you have a condition that you can't recover
> from without reboot.

Not if the postmaster outputs the following:

> What I'm currently imagining is that the stub implementations will just
> return a failure code for IPC_STAT, and the outer code will in turn fail
> with a message along the lines of "It looks like there's a pre-existing
> shmem block (id XXX) still in use. If you're sure there are no old
> backends still running, remove the shmem block with ipcrm(1), or just
> delete $PGDATA/postmaster.pid." I dunno what shmem management tools
> exist on BeOS/QNX, but deleting the lockfile will definitely suppress
> the startup interlock ;-).
>
> > Yes, if possible a more meaningfull error message and pointer to
> > some docco would be nice
>
> Is the above good enough?

Sure. :)

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