Re: Leader backend hang on IPC/ParallelFinish when LWLock held at parallel query start

Noah Misch <noah(at)leadboat(dot)com> writes:
> What if we just ignored the plancache when uninterruptible? The new planner
> check would then suffice.

Only if you believe that parallel-query is the only problem,
which is something I seriously doubt. I fear that the
committed patch is just a band-aid over one symptom of the
general problem that we can't permit arbitrary operations
to be invoked from a btree comparison function. It's late
here so I'm not sufficiently awake to think of examples,
but I'm sure there are some.

However ... clearly a maliciously-coded btree support function can
do arbitrarily bad stuff. We restrict creation of opclasses to
superusers for exactly that reason. If our ambitions are only
to prevent support functions from *accidentally* causing problems,
is disabling parallel query enough? I'm still pretty uncomfortable
about it, but it's less obviously insufficient than in the general
case.

regards, tom lane