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

Alfred Perlstein <bright@wintelcom.net> writes:
> * Tom Lane <tgl@sss.pgh.pa.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.

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?
        regards, tom lane