Re: [HACKERS] Proposal for async support in libpq

Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> You supply the indication to the backend, and I will see that the
> backend processes it properly.

You're on ;-)

Signaling the cancel request via OOB sounds reasonable, as long as
nothing else is using it and all the systems we care about support it.
(I see a couple of routines to support OOB data in
src/backend/libpq/pqcomm.c, but they don't seem to be called from
anywhere. Vestiges of an old protocol, perhaps?)

I still need to understand better what the backend will send back
in response to a cancel request, especially if it's idle by the
time the request arrives. Will that result in an asynchronous error
response of some sort? Do I need to make said response visible to
the frontend application? (Probably not ... it will have already
discovered that the query completed normally.)

How should cancellation interact with copy in/out?

These are mostly documentation issues, rather than stuff that directly
affects code in libpq, but we ought to nail it down.

regards, tom lane