RE: Transactions involving multiple postgres foreign servers, take 2

From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
> It seems to respond to a statement-cancel signal immediately while
> waiting for a coming byte.  However, seems to wait forever while
> waiting a space in send-buffer. (Is that mean the session will be
> stuck if it sends a large chunk of bytes while the network is down?)

What part makes you worried about that?  libpq's send processing?

I've just examined pgfdw_cancel_query(), too.  As below, it uses a hidden 30 second timeout.  After all, postgres_fdw
alsorelies on timeout already. 

    /*
     * If it takes too long to cancel the query and discard the result, assume
     * the connection is dead.
     */
    endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000);


> After receiving a signal, it closes the problem connection. So the
> local session is usable after that but the fiailed remote sessions are
> closed and created another one at the next use.

I couldn't see that the problematic connection is closed when the cancellation fails... Am I looking at a wrong place?

                    /*
                     * If connection is already unsalvageable, don't touch it
                     * further.
                     */
                    if (entry->changing_xact_state)
                        break;


Regards
Takayuki Tsunakawa