On Sat, Jul 21, 2012 at 5:36 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Martijn van Oosterhout <klep...@svana.org> writes: >> On Sat, Jul 21, 2012 at 01:08:58AM +0100, Daniele Varrazzo wrote: >>> In a libpq application, if there is an application error between >>> PQsendQuery and PQgetResult, is there a way to revert a connection >>> back to an usable state (i.e. from transaction status ACTIVE to IDLE) >>> without using the network in a blocking way? We are currently doing > >> There is PQreset(), which also exists in a non-blocking variant. > > Note that PQreset essentially kills the connection and establishes a new > one, which might not be what Daniele is looking for. The alternative > approach is to issue PQcancel and then just let the query flush out as > you normally would in an async application, ie PQisBusy/PQconsumeInput > until ready, then PQgetResult (which you throw away), repeat until you > get NULL.
I'm back on this issue. I've tested the PQcancel approach, but blocks as well on send()/recv(), and given the constraint resources it is bound to use (to be called from a signal handler) I assume there is no workaround for it. The PQreset approach has the shortcoming of discarding the session configuration that somebody may have created in Pythonland: a state with a connection made but not configured would be something a client program is probably not prepared to handle. I think a plain disconnection would be much easier to handle for long-running python program: a long-running one should probably already cope with a broken connection, a short-lived one would benefit of working SIGINT. If you have other suggestions I'd be glad to know, thank you. -- Daniele -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers