> I have experienced a server crash when deleting from a table that ahs a
> before trigger on it. The before trigger calls a function that deletes from
> a foreign (informix) table.
Hm, can you get a stack trace from that?
https://wiki.postgresql.org/wiki/Generating_a_stack_trace_of_a_PostgreSQL_backend
It seems fairly likely that the bug is in whatever FDW you're using
rather than in core Postgres. A stack trace would help to
confirm or refute that.
regards, tom lane