From 3483bb99eb1329f4ac90bcb8b8a04ec1a7ab6045 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Sun, 11 Jun 2017 18:22:29 -0700
Subject: [PATCH] Minimal infrastructure for per-backend citus initialization.

---
 src/backend/distributed/shared_library_init.c  | 17 ++++++++++++++++-
 src/backend/distributed/utils/metadata_cache.c |  8 ++++++++
 src/include/distributed/shared_library_init.h  | 16 ++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 src/include/distributed/shared_library_init.h

diff --git a/src/backend/distributed/shared_library_init.c b/src/backend/distributed/shared_library_init.c
index 181242e8b..f6a03702b 100644
--- a/src/backend/distributed/shared_library_init.c
+++ b/src/backend/distributed/shared_library_init.c
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * shared_library_init.c
- *	  Initialize Citus extension
+ *	  Functionality related to the initialization of the Citus extension.
  *
  * Copyright (c) 2012-2016, Citus Data, Inc.
  *-------------------------------------------------------------------------
@@ -36,6 +36,7 @@
 #include "distributed/pg_dist_partition.h"
 #include "distributed/placement_connection.h"
 #include "distributed/remote_commands.h"
+#include "distributed/shared_library_init.h"
 #include "distributed/task_tracker.h"
 #include "distributed/transaction_management.h"
 #include "distributed/worker_manager.h"
@@ -177,6 +178,20 @@ _PG_init(void)
 }
 
 
+/*
+ * StartupCitusBackend initializes per-backend infrastructure, and is called
+ * the first time citus is used in a database.
+ *
+ * NB: All code here has to be able to cope with this routine being called
+ * multiple times in the same backend.  This will e.g. happen when the
+ * extension is created or upgraded.
+ */
+void
+StartupCitusBackend(void)
+{
+}
+
+
 /*
  * CreateRequiredDirectories - Create directories required for Citus to
  * function.
diff --git a/src/backend/distributed/utils/metadata_cache.c b/src/backend/distributed/utils/metadata_cache.c
index d0ec677bf..9dd62087e 100644
--- a/src/backend/distributed/utils/metadata_cache.c
+++ b/src/backend/distributed/utils/metadata_cache.c
@@ -35,6 +35,7 @@
 #include "distributed/pg_dist_partition.h"
 #include "distributed/pg_dist_shard.h"
 #include "distributed/pg_dist_shard_placement.h"
+#include "distributed/shared_library_init.h"
 #include "distributed/shardinterval_utils.h"
 #include "distributed/worker_manager.h"
 #include "distributed/worker_protocol.h"
@@ -1118,6 +1119,13 @@ CitusHasBeenLoaded(void)
 			{
 				extensionScriptExecuted = false;
 			}
+
+			/*
+			 * Whenever the extension exists, even when currently creating it,
+			 * we need the infrastructure to run citus in this database to be
+			 * ready.
+			 */
+			StartupCitusBackend();
 		}
 
 		/* we disable extension features during pg_upgrade */
diff --git a/src/include/distributed/shared_library_init.h b/src/include/distributed/shared_library_init.h
new file mode 100644
index 000000000..35f3d0e16
--- /dev/null
+++ b/src/include/distributed/shared_library_init.h
@@ -0,0 +1,16 @@
+/*-------------------------------------------------------------------------
+ *
+ * shared_library_init.h
+ *	  Functionality related to the initialization of the Citus extension.
+ *
+ * Copyright (c) 2017, Citus Data, Inc.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef SHARED_LIBRARY_INIT_H
+#define SHARED_LIBRARY_INIT_H
+
+extern void StartupCitusBackend(void);
+
+#endif /* SHARED_LIBRARY_INIT_H */