From da11d22a5ed78a690ccdbfeb77c59749c541d463 Mon Sep 17 00:00:00 2001
From: Arseny Sher <sher-ars@yandex.ru>
Date: Sun, 17 Mar 2019 07:42:18 +0300
Subject: [PATCH] Allow parallel workers while backends are alive in 'smart'
 shutdown.

Since postmaster doesn't advertise that he is never going to start parallel
workers after shutdown was issued, parallel leader stucks waiting for them
indefinitely.
---
 src/backend/postmaster/postmaster.c | 44 ++++++++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index fe599632d3..d60969fdb8 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -2689,10 +2689,30 @@ pmdie(SIGNAL_ARGS)
 			if (pmState == PM_RUN || pmState == PM_RECOVERY ||
 				pmState == PM_HOT_STANDBY || pmState == PM_STARTUP)
 			{
+				slist_iter siter;
+
+				/*
+				 * Shut down all bgws except parallel workers: graceful
+				 * termination of existing sessions needs them.
+				 */
+				slist_foreach(siter, &BackgroundWorkerList)
+				{
+					RegisteredBgWorker *rw;
+
+					rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
+					if (rw->rw_pid > 0 &&
+						((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0))
+					{
+						ereport(DEBUG4,
+								(errmsg_internal("sending signal %d to process %d",
+												 SIGTERM, (int) rw->rw_pid)));
+						signal_child(rw->rw_pid, SIGTERM);
+
+					}
+				}
+
 				/* autovac workers are told to shut down immediately */
-				/* and bgworkers too; does this need tweaking? */
-				SignalSomeChildren(SIGTERM,
-								   BACKEND_TYPE_AUTOVAC | BACKEND_TYPE_BGWORKER);
+				SignalSomeChildren(SIGTERM, BACKEND_TYPE_AUTOVAC);
 				/* and the autovac launcher too */
 				if (AutoVacPID != 0)
 					signal_child(AutoVacPID, SIGTERM);
@@ -5735,18 +5755,30 @@ do_start_bgworker(RegisteredBgWorker *rw)
  * specified start_time?
  */
 static bool
-bgworker_should_start_now(BgWorkerStartTime start_time)
+bgworker_should_start_now(RegisteredBgWorker *rw)
 {
+	BgWorkerStartTime start_time = rw->rw_worker.bgw_start_time;
+
 	switch (pmState)
 	{
 		case PM_NO_CHILDREN:
 		case PM_WAIT_DEAD_END:
 		case PM_SHUTDOWN_2:
 		case PM_SHUTDOWN:
+			return false;
+
 		case PM_WAIT_BACKENDS:
 		case PM_WAIT_READONLY:
 		case PM_WAIT_BACKUP:
-			break;
+			/*
+			 * Allow new parallel workers in SmartShutdown while backends
+			 * are still there.
+			 */
+			if (((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0) ||
+				Shutdown != SmartShutdown ||
+				FatalError)
+				return false;
+			/* fall through */
 
 		case PM_RUN:
 			if (start_time == BgWorkerStart_RecoveryFinished)
@@ -5906,7 +5938,7 @@ maybe_start_bgworkers(void)
 			}
 		}
 
-		if (bgworker_should_start_now(rw->rw_worker.bgw_start_time))
+		if (bgworker_should_start_now(rw))
 		{
 			/* reset crash time before trying to start worker */
 			rw->rw_crashed_at = 0;
-- 
2.11.0