commit 5865a275eca08ca525b140ad3b61ea9b88276295
Author: kuroda.hayato%40jp.fujitsu.com <kuroda.hayato@jp.fujitsu.com>
Date:   Wed Sep 1 09:22:42 2021 +0000

    postgres_fdw: Add application_name GUC

diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c
index 82aa14a65d..af9ae8bc7d 100644
--- a/contrib/postgres_fdw/connection.c
+++ b/contrib/postgres_fdw/connection.c
@@ -353,10 +353,11 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
 		/*
 		 * Construct connection params from generic options of ForeignServer
 		 * and UserMapping.  (Some of them might not be libpq options, in
-		 * which case we'll just waste a few array slots.)  Add 3 extra slots
-		 * for fallback_application_name, client_encoding, end marker.
+		 * which case we'll just waste a few array slots.)  Add 4 extra slots
+		 * for application_name, fallback_application_name, client_encoding,
+		 * end marker.
 		 */
-		n = list_length(server->options) + list_length(user->options) + 3;
+		n = list_length(server->options) + list_length(user->options) + 4;
 		keywords = (const char **) palloc(n * sizeof(char *));
 		values = (const char **) palloc(n * sizeof(char *));
 
@@ -366,7 +367,14 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
 		n += ExtractConnectionOptions(user->options,
 									  keywords + n, values + n);
 
-		/* Use "postgres_fdw" as fallback_application_name. */
+		/* Use GUC paramter if set */
+		if (pgfdw_application_name && *pgfdw_application_name != '\0')
+		{
+			keywords[n] = "application_name";
+			values[n] = pgfdw_application_name;
+			n++;
+		}
+		/* Use "postgres_fdw" as fallback_application_name */
 		keywords[n] = "fallback_application_name";
 		values[n] = "postgres_fdw";
 		n++;
diff --git a/contrib/postgres_fdw/option.c b/contrib/postgres_fdw/option.c
index c574ca2cf3..da693cb74c 100644
--- a/contrib/postgres_fdw/option.c
+++ b/contrib/postgres_fdw/option.c
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * option.c
- *		  FDW option handling for postgres_fdw
+ *		  FDW and GUC option handling for postgres_fdw
  *
  * Portions Copyright (c) 2012-2021, PostgreSQL Global Development Group
  *
@@ -18,6 +18,7 @@
 #include "catalog/pg_user_mapping.h"
 #include "commands/defrem.h"
 #include "commands/extension.h"
+#include "common/string.h"
 #include "postgres_fdw.h"
 #include "utils/builtins.h"
 #include "utils/guc.h"
@@ -52,6 +53,18 @@ static void InitPgFdwOptions(void);
 static bool is_valid_option(const char *keyword, Oid context);
 static bool is_libpq_option(const char *keyword);
 
+/*
+ * GUC parameters
+ */
+char* pgfdw_application_name = NULL;
+
+/*
+ * _PG_init() and check hook
+ */
+
+static bool check_pgfdw_application_name(char **newval, void **extra, GucSource source);
+void _PG_init(void);
+
 #include "miscadmin.h"
 
 /*
@@ -435,3 +448,33 @@ ExtractExtensionList(const char *extensionsString, bool warnOnMissing)
 	list_free(extlist);
 	return extensionOids;
 }
+
+/*
+ * Completely same as server-side.
+ */
+static bool
+check_pgfdw_application_name(char **newval, void **extra, GucSource source)
+{
+	/* Only allow clean ASCII chars in the application name */
+	if (*newval)
+		pg_clean_ascii(*newval);
+	return true;
+}
+
+/*
+ * Define GUC parameters.
+ */
+void
+_PG_init(void)
+{
+	DefineCustomStringVariable("postgres_fdw.application_name",
+							   "Sets the application name. This is used when connects to the remote server.",
+							   NULL,
+							   &pgfdw_application_name,
+							   NULL,
+							   PGC_USERSET,
+							   GUC_IS_NAME,
+							   check_pgfdw_application_name,
+							   NULL,
+							   NULL);
+}
diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index ca83306af9..90b72e9ec5 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -158,6 +158,7 @@ extern int	ExtractConnectionOptions(List *defelems,
 									 const char **values);
 extern List *ExtractExtensionList(const char *extensionsString,
 								  bool warnOnMissing);
+extern char *pgfdw_application_name;
 
 /* in deparse.c */
 extern void classifyConditions(PlannerInfo *root,
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml
index 0075bc3dbb..caa10519e0 100644
--- a/doc/src/sgml/postgres-fdw.sgml
+++ b/doc/src/sgml/postgres-fdw.sgml
@@ -105,6 +105,29 @@
   of columns to the remote table is by name, not position.
  </para>
 
+ <sect2>
+  <title> Configuration Parameters </title>
+  <variablelist>
+   <varlistentry>
+    <term>
+     <varname>postgres_fdw.application_name</varname> (<type>string</type>)
+     <indexterm>
+      <primary>
+       <varname>postgres_fdw.application_name</varname> configuration parameter
+      </primary>
+     </indexterm>
+    </term>
+    <listitem>
+     <para>
+      Specifies a value for <xref linkend="guc-application-name"/>
+      configuration parameter. This value is used only when a backend process
+      starts to establish the remote connection. 
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </sect2>
+
  <sect2>
   <title>FDW Options of postgres_fdw</title>