Detect POLLHUP/POLLRDHUP while running queries.

Provide a new GUC check_client_connection_interval that can be used to
check whether the client connection has gone away, while running very
long queries.  It is disabled by default.

For now this uses a non-standard Linux extension (also adopted by at
least one other OS).  POLLRDHUP is not defined by POSIX, and other OSes
don't have a reliable way to know if a connection was closed without
actually trying to read or write.

In future we might consider trying to send a no-op/heartbeat message
instead, but that could require protocol changes.

Author: Sergey Cherkashin <[email protected]>
Author: Thomas Munro <[email protected]>
Reviewed-by: Thomas Munro <[email protected]>
Reviewed-by: Tatsuo Ishii <[email protected]>
Reviewed-by: Konstantin Knizhnik <[email protected]>
Reviewed-by: Zhihong Yu <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Maksim Milyutin <[email protected]>
Reviewed-by: Tsunakawa, Takayuki/綱川 貴之 <[email protected]>
Reviewed-by: Tom Lane <[email protected]> (much earlier version)
Discussion: https://postgr.es/m/77def86b27e41f0efcba411460e929ae%40postgrespro.ru

1 files changed, 32 insertions, 0 deletions

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 2b1b68109fd..ad351e2fd1e 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -102,6 +102,9 @@ int			max_stack_depth = 100;
 /* wait N seconds to allow attach from a debugger */
 int			PostAuthDelay = 0;
 
+/* Time between checks that the client is still connected. */
+int			client_connection_check_interval = 0;
+
 /* ----------------
  *		private typedefs etc
  * ----------------
@@ -2671,6 +2674,14 @@ start_xact_command(void)
 	 * not desired, the timeout has to be disabled explicitly.
 	 */
 	enable_statement_timeout();
+
+	/* Start timeout for checking if the client has gone away if necessary. */
+	if (client_connection_check_interval > 0 &&
+		IsUnderPostmaster &&
+		MyProcPort &&
+		!get_timeout_active(CLIENT_CONNECTION_CHECK_TIMEOUT))
+		enable_timeout_after(CLIENT_CONNECTION_CHECK_TIMEOUT,
+							 client_connection_check_interval);
 }
 
 static void
@@ -3149,6 +3160,27 @@ ProcessInterrupts(void)
 					(errcode(ERRCODE_ADMIN_SHUTDOWN),
 					 errmsg("terminating connection due to administrator command")));
 	}
+
+	if (CheckClientConnectionPending)
+	{
+		CheckClientConnectionPending = false;
+
+		/*
+		 * Check for lost connection and re-arm, if still configured, but not
+		 * if we've arrived back at DoingCommandRead state.  We don't want to
+		 * wake up idle sessions, and they already know how to detect lost
+		 * connections.
+		 */
+		if (!DoingCommandRead && client_connection_check_interval > 0)
+		{
+			if (!pq_check_connection())
+				ClientConnectionLost = true;
+			else
+				enable_timeout_after(CLIENT_CONNECTION_CHECK_TIMEOUT,
+									 client_connection_check_interval);
+		}
+	}
+
 	if (ClientConnectionLost)
 	{
 		QueryCancelPending = false; /* lost connection trumps QueryCancel */