On 1/22/18 21:33, Craig Ringer wrote: > We don't have much in the way of rules about what input functions can or > cannot do, so you can't assume much about their behaviour and what must > / must not be cleaned up. Nor can you just reset the state in a heavy > handed manner like (say) plpgsql does.
I think one thing to try would to define a special kind of exception that can safely be caught and ignored. Then, input functions can communicate benign parse errors by doing their own cleanup first, then throwing this exception, and then the COPY subsystem can deal with it.
That makes sense. We'd only use the error code range in question when it was safe to catch without re-throw, and we'd have to enforce rules around using a specific memory context. Of course no LWLocks could be held, but that's IIRC true when throwing anyway unless you plan to proc_exit() in your handler.
People will immediately ask for it to handle RI errors too, so something similar would be needed there. But frankly, Pg's RI handling for bulk loading desperately needs a major change in how it works to make it efficient anyway, the current model of individual row triggers is horrible for bulk load performance.
