postgres_fdw: Make postgres_fdw.application_name support more escape sequences.

Commit 6e0cb3dec1 allowed postgres_fdw.application_name to include
escape sequences %a (application name), %d (database name), %u (user name)
and %p (pid). In addition to them, this commit makes it support
the escape sequences for session ID (%c) and cluster name (%C).
These are helpful to investigate where each remote transactions came from.

Author: Fujii Masao
Reviewed-by: Ryohei Takahashi, Kyotaro Horiguchi
Discussion: https://postgr.es/m/1041dc9a-c976-049f-9f14-e7d94c29c4b2@oss.nttdata.com

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -10910,6 +10910,26 @@ SELECT pg_terminate_backend(pid, 180000) FROM pg_stat_activity
  t
 (1 row)
 
+-- Test %c (session ID) and %C (cluster name) escape sequences.
+SET postgres_fdw.application_name TO 'fdw_%C%c';
+SELECT 1 FROM ft6 LIMIT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+  WHERE application_name =
+    substring('fdw_' || current_setting('cluster_name') ||
+      to_hex(trunc(EXTRACT(EPOCH FROM (SELECT backend_start FROM
+      pg_stat_get_activity(pg_backend_pid()))))::integer) || '.' ||
+      to_hex(pg_backend_pid())
+      for current_setting('max_identifier_length')::int);
+ pg_terminate_backend 
+----------------------
+ t
+(1 row)
+
 --Clean up
 RESET postgres_fdw.application_name;
 RESET debug_discard_caches;

contrib/postgres_fdw/option.c

@@ -489,6 +489,12 @@ process_pgfdw_appname(const char *appname)
 			case 'a':
 				appendStringInfoString(&buf, application_name);
 				break;
+			case 'c':
+				appendStringInfo(&buf, "%lx.%x", (long) (MyStartTime), MyProcPid);
+				break;
+			case 'C':
+				appendStringInfoString(&buf, cluster_name);
+				break;
 			case 'd':
 				appendStringInfoString(&buf, MyProcPort->database_name);
 				break;

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -3501,6 +3501,17 @@ SELECT pg_terminate_backend(pid, 180000) FROM pg_stat_activity
     substring('fdw_' || current_setting('application_name') ||
       CURRENT_USER || '%' for current_setting('max_identifier_length')::int);
 
+-- Test %c (session ID) and %C (cluster name) escape sequences.
+SET postgres_fdw.application_name TO 'fdw_%C%c';
+SELECT 1 FROM ft6 LIMIT 1;
+SELECT pg_terminate_backend(pid, 180000) FROM pg_stat_activity
+  WHERE application_name =
+    substring('fdw_' || current_setting('cluster_name') ||
+      to_hex(trunc(EXTRACT(EPOCH FROM (SELECT backend_start FROM
+      pg_stat_get_activity(pg_backend_pid()))))::integer) || '.' ||
+      to_hex(pg_backend_pid())
+      for current_setting('max_identifier_length')::int);
+
 --Clean up
 RESET postgres_fdw.application_name;
 RESET debug_discard_caches;

doc/src/sgml/postgres-fdw.sgml

@@ -984,6 +984,20 @@ postgres=# SELECT postgres_fdw_disconnect_all();
          <entry><literal>%a</literal></entry>
          <entry>Application name on local server</entry>
         </row>
+        <row>
+         <entry><literal>%c</literal></entry>
+         <entry>
+          Session ID on local server
+          (see <xref linkend="guc-log-line-prefix"/> for details)
+         </entry>
+        </row>
+        <row>
+         <entry><literal>%C</literal></entry>
+         <entry>
+          Cluster name in local server
+          (see <xref linkend="guc-cluster-name"/> for details)
+         </entry>
+        </row>
         <row>
          <entry><literal>%u</literal></entry>
          <entry>User name on local server</entry>

src/include/utils/guc.h

@@ -271,7 +271,7 @@ extern int	temp_file_limit;
 
 extern int	num_temp_buffers;
 
-extern char *cluster_name;
+extern PGDLLIMPORT char *cluster_name;
 extern PGDLLIMPORT char *ConfigFileName;
 extern char *HbaFileName;
 extern char *IdentFileName;