Kai Kratz <kai(dot)kratz(at)googlemail(dot)com> writes:
> It is an in-house developed FDW. Part of the surprise was that we
> execute the postgres integration tests (as described here:
> https://www.postgresql.org/docs/current/static/regress-run.html)
> against a postgres instance with our custom FDW loaded and no errors
> show up.
Well, actually, it *is* pretty surprising that an FDW would affect
the behavior of ALTER FUNCTION. Are you perhaps also hooking into
some parser hooks, or something else that's outside the FDW API?
Could you show us a backtrace from the segfault?
regards, tom lane