fix_drop_subscription_hang.patch

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 9467f58a23d..9f2f1abb586 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1575,7 +1575,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * Lock pg_subscription with AccessExclusiveLock to ensure that the
 	 * launcher doesn't restart new worker during dropping the subscription
 	 */
-	rel = table_open(SubscriptionRelationId, AccessExclusiveLock);
+	rel = table_open(SubscriptionRelationId, AccessShareLock);
 
 	tup = SearchSysCache2(SUBSCRIPTIONNAME, MyDatabaseId,
 						  CStringGetDatum(stmt->subname));
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 294d0d74d8c..bdce4467553 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -35,6 +35,7 @@
 #include "replication/walreceiver.h"
 #include "replication/worker_internal.h"
 #include "storage/ipc.h"
+#include "storage/lmgr.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "tcop/tcopprot.h"
@@ -171,6 +172,43 @@ get_subscription_list(void)
 	return res;
 }
 
+/*
+ * Check subscription exists or not.
+ */
+static bool
+is_subscription_exist(Oid subid)
+{
+	Relation	rel;
+	TableScanDesc scan;
+	HeapTuple	tup;
+	bool		found = false;
+
+	/* Start a transaction, for detail see comments in get_subscription_list */
+	StartTransactionCommand();
+	(void) GetTransactionSnapshot();
+
+	rel = table_open(SubscriptionRelationId, AccessShareLock);
+	scan = table_beginscan_catalog(rel, 0, NULL);
+
+	while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+	{
+		Form_pg_subscription subform = (Form_pg_subscription) GETSTRUCT(tup);
+
+		if (subform->oid == subid)
+		{
+			found = true;
+			break;
+		}
+	}
+
+	table_endscan(scan);
+	table_close(rel, AccessShareLock);
+
+	CommitTransactionCommand();
+
+	return found;
+}
+
 /*
  * Wait for a background worker to start up and attach to the shmem context.
  *
@@ -1209,6 +1247,19 @@ ApplyLauncherMain(Datum main_arg)
 			if (last_start == 0 ||
 				(elapsed = TimestampDifferenceMilliseconds(last_start, now)) >= wal_retrieve_retry_interval)
 			{
+				/*
+				 * Lock the subscription to prevent it from being concurrently dropped,
+				 * then re-verify its existence.
+				 */
+				LockSharedObject(SubscriptionRelationId, sub->oid, 0,
+								 AccessShareLock);
+				if (!is_subscription_exist(sub->oid))
+				{
+					UnlockSharedObject(SubscriptionRelationId, sub->oid, 0,
+									   AccessShareLock);
+					continue;
+				}
+
 				ApplyLauncherSetWorkerStartTime(sub->oid, now);
 				if (!logicalrep_worker_launch(WORKERTYPE_APPLY,
 											  sub->dbid, sub->oid, sub->name,
@@ -1225,6 +1276,8 @@ ApplyLauncherMain(Datum main_arg)
 					wait_time = Min(wait_time,
 									wal_retrieve_retry_interval);
 				}
+				UnlockSharedObject(SubscriptionRelationId, sub->oid, 0,
+								   AccessShareLock);
 			}
 			else
 			{