From ed58a404d59bb8baaa0f9d3a2543d31586e30965 Mon Sep 17 00:00:00 2001
From: Onder Kalaci <onderkalaci@gmail.com>
Date: Thu, 14 Jan 2021 19:10:44 +0300
Subject: [PATCH] Release lock on CoordinatorAddedAsWorkerNode()

Because master_add_node(or others) might acquire ExclusiveLock
and their initiated sessions may call CoordinatorAddedAsWorkerNode().

With this we prevent potential deadlocks.
---
 src/backend/distributed/commands/table.c                 | 4 ++--
 src/backend/distributed/operations/worker_node_manager.c | 6 +-----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/src/backend/distributed/commands/table.c b/src/backend/distributed/commands/table.c
index 95a8cb0e8..09b205851 100644
--- a/src/backend/distributed/commands/table.c
+++ b/src/backend/distributed/commands/table.c
@@ -413,8 +413,8 @@ PreprocessAlterTableStmt(Node *node, const char *alterTableCommand,
 	}
 
 	if (processUtilityContext != PROCESS_UTILITY_SUBCOMMAND &&
-		AlterTableDefinesFKeyBetweenPostgresAndNonDistTable(alterTableStatement) &&
-		CoordinatorAddedAsWorkerNode())
+		CoordinatorAddedAsWorkerNode() &&
+		AlterTableDefinesFKeyBetweenPostgresAndNonDistTable(alterTableStatement))
 	{
 		/*
 		 * We don't process subcommands generated by postgres.
diff --git a/src/backend/distributed/operations/worker_node_manager.c b/src/backend/distributed/operations/worker_node_manager.c
index a1637bf34..12d3bdf06 100644
--- a/src/backend/distributed/operations/worker_node_manager.c
+++ b/src/backend/distributed/operations/worker_node_manager.c
@@ -418,17 +418,13 @@ NodeIsPrimaryWorker(WorkerNode *node)
 
 /*
  * CoordinatorAddedAsWorkerNode returns true if coordinator is added to the
- * pg_dist_node. This function also acquires ShareLock on pg_dist_node
- * and does not release it to ensure that existency of the coordinator in
- * metadata won't be changed until the end of transaction.
+ * pg_dist_node.
  */
 bool
 CoordinatorAddedAsWorkerNode()
 {
 	bool groupContainsNodes = false;
 
-	LockRelationOid(DistNodeRelationId(), ShareLock);
-
 	PrimaryNodeForGroup(COORDINATOR_GROUP_ID, &groupContainsNodes);
 
 	return groupContainsNodes;