RE: Add client connection check during the execution of the query

From: Thomas Munro <thomas.munro@gmail.com>
> I changed my mind.  Let's commit the pleasingly simple Linux-only feature for
> now, and extend to it to send some kind of no-op message in a later release.
> So this is the version I'd like to go with.
> Objections?

+1, as some of our users experienced the problem that the server kept processing (IIRC, a buggy PL/pgSQL procedure that loops indefinitely) after they killed the client.

TBH, Linux and Windows will be sufficient.  But I'm for providing a good feature on a specific OS first.


(1)
+	rc = poll(&pollfd, 1, 0);
+	if (rc < 0)
+	{
+		elog(COMMERROR, "could not poll socket: %m");
+		return false;

I think it's customary to use ereport() and errcode_for_socket_access().


(2)
pq_check_connection()

Following PostmasterIsAlive(), maybe it's better to name it as pq_connection_is_alive() pq_client_is_alive(), or pq_frontend_is_alive() like the pqcomm.c's head comment uses the word frontend?


(3)
 #include <limits.h>
+#include <poll.h>
 #ifndef WIN32
 #include <sys/mman.h>
 #endif

poll.h should be included between #ifndef WIN32 and #endif?


(4)
I think the new GUC works for walsender as well.  If so, how do we explain the relationship between the new GUC and wal_receiver_timeout and recommend the settings of them?


Regards
Takayuki Tsunakawa