postgres_fdw: Allow postgres_fdw.application_name to include escape sequences.

application_name that used when postgres_fdw establishes a connection to
a foreign server can be specified in either or both a connection parameter
of a server object and GUC postgres_fdw.application_name. This commit
allows those parameters to include escape sequences that begins with
% character. Then postgres_fdw replaces those escape sequences with
status information. For example, %d and %u are replaced with user name
and database name in local server, respectively. This feature enables us
to add information more easily to track remote transactions or queries,
into application_name of a remote connection.

Author: Hayato Kuroda
Reviewed-by: Kyotaro Horiguchi, Masahiro Ikeda, Hou Zhijie, Fujii Masao
Discussion: https://postgr.es/m/TYAPR01MB5866FAE71C66547C64616584F5EB9@TYAPR01MB5866.jpnprd01.prod.outlook.com
Discussion: https://postgr.es/m/TYCPR01MB5870D1E8B949DAF6D3B84E02F5F29@TYCPR01MB5870.jpnprd01.prod.outlook.com

1 files changed, 32 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 7720ab9c581..6ce7ec24f08 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -10825,3 +10825,35 @@ ERROR:  invalid value for integer option "batch_size": 100$%$#$#
 ALTER FOREIGN DATA WRAPPER postgres_fdw OPTIONS (nonexistent 'fdw');
 ERROR:  invalid option "nonexistent"
 HINT:  There are no valid options in this context.
+-- ===================================================================
+-- test postgres_fdw.application_name GUC
+-- ===================================================================
+-- Close all the existing cached connections so that new connection
+-- will be established with new setting of postgres_fdw.application_name.
+SELECT 1 FROM postgres_fdw_disconnect_all();
+ ?column? 
+----------
+        1
+(1 row)
+
+-- Add some escape sequences into postgres_fdw.application_name
+-- so as to test that they are replaced with status information expectedly.
+SET postgres_fdw.application_name TO '%a%u%d%p%%';
+BEGIN;
+SELECT 1 FROM ft6 LIMIT 1;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT count(*) FROM pg_stat_activity
+  WHERE application_name = current_setting('application_name') ||
+    CURRENT_USER || current_database() || pg_backend_pid() || '%';
+ count 
+-------
+     1
+(1 row)
+
+COMMIT;
+--Clean up
+RESET postgres_fdw.application_name;