Re: Speed dblink using alternate libpq tuple storage

On Wed, Apr 04, 2012 at 06:41:00PM -0400, Tom Lane wrote:
> Marko Kreen <markokr(at)gmail(dot)com> writes:
> > On Wed, Apr 4, 2012 at 10:17 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> Given the lack of consensus around the suspension API, maybe the best
> >> way to get the underlying libpq patch to a committable state is to take
> >> it out --- that is, remove the "return zero" option for row processors.
>
> > Agreed.
>
> Done that way.

Minor cleanups:

* Change callback return value to be 'bool': 0 is error.
Currently the accepted return codes are 1 and -1,
which is weird.

If we happen to have the 'early-exit' logic in the future,
it should not work via callback return code. So keeping the 0
in reserve is unnecessary.

* Support exceptions in multi-statement PQexec() by storing
finished result under PGconn temporarily. Without doing it,
the result can leak if callback longjmps while processing
next result.

* Add <caution> to docs for permanently keeping custom callback.

This API fragility is also reason why early-exit (if it appears)
should not work via callback - instead it should give safer API.

--
marko