Re: [HACKERS] Proposal for async support in libpq

> 
> Bruce Momjian <maillist@candle.pha.pa.us> writes:
> > This all looks good.  Another thing we really need it to be able to
> > cancel queries.  This would be a big win, and looks like it could fit
> > into the scheme here.
> 
> I thought about proposing a PQcancelAsync that would cancel the active
> query-in-progress.  But that would require support on the backend side,
> and I am far from competent to make it happen.  (libpq is simple enough
> that I'm not afraid to rewrite it, but making major mods to the backend
> is another story.  I just got here this week...)

In backend/libpq/pqcomm.c, I see pg_sendoob() which sends out-of-band
data FROM the backend TO the client, but it is not called from anywhere.

This could be a method of signaling that a notification was pending, and
sending out-of-band data FROm the client TO the backend could be used
for cancelling a query.

out-of-band data causes a convenient signal to the process on the other
end, which can easily be used to handle these cases.

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