From dc370335a9a3b2b0f90a9cb3140d64377d1f6903 Mon Sep 17 00:00:00 2001
From: Onder Kalaci <onderkalaci@gmail.com>
Date: Wed, 26 Jan 2022 16:57:08 +0100
Subject: [PATCH] Use a fixed application_name while connecting to remote nodes

Citus heavily relies on application_name, see
`IsCitusInitiatedRemoteBackend()`.

But if the user set the application name, such as export PGAPPNAME=test_name,
Citus uses that name while connecting to the remote node.

With this commit, we ensure that Citus always connects with
the "citus" user name to the remote nodes.
---
 .../connection/connection_configuration.c          | 12 ++++++------
 src/test/regress/expected/mx_application_name.out  | 14 ++++++++++++++
 src/test/regress/multi_mx_schedule                 |  1 +
 src/test/regress/sql/mx_application_name.sql       | 14 ++++++++++++++
 4 files changed, 35 insertions(+), 6 deletions(-)
 create mode 100644 src/test/regress/expected/mx_application_name.out
 create mode 100644 src/test/regress/sql/mx_application_name.sql

diff --git a/src/backend/distributed/connection/connection_configuration.c b/src/backend/distributed/connection/connection_configuration.c
index a0bd31e25..32dc21e40 100644
--- a/src/backend/distributed/connection/connection_configuration.c
+++ b/src/backend/distributed/connection/connection_configuration.c
@@ -72,8 +72,8 @@ InitConnParams()
 /*
  * ResetConnParams frees all strings in the keywords and parameters arrays,
  * sets their elements to null, and resets the ConnParamsSize to zero before
- * adding back any hardcoded global connection settings (at present, only the
- * fallback_application_name of 'citus').
+ * adding back any hardcoded global connection settings (at present, there
+ * are no).
  */
 void
 ResetConnParams()
@@ -89,8 +89,6 @@ ResetConnParams()
 	ConnParams.size = 0;
 
 	InvalidateConnParamsHashEntries();
-
-	AddConnParam("fallback_application_name", CITUS_APPLICATION_NAME);
 }
 
 
@@ -253,14 +251,16 @@ GetConnParams(ConnectionHashKey *key, char ***keywords, char ***values,
 		"port",
 		"dbname",
 		"user",
-		"client_encoding"
+		"client_encoding",
+		"application_name"
 	};
 	const char *runtimeValues[] = {
 		key->hostname,
 		nodePortString,
 		key->database,
 		key->user,
-		GetDatabaseEncodingName()
+		GetDatabaseEncodingName(),
+		CITUS_APPLICATION_NAME
 	};
 
 	/*
diff --git a/src/test/regress/expected/mx_application_name.out b/src/test/regress/expected/mx_application_name.out
new file mode 100644
index 000000000..f35f29d29
--- /dev/null
+++ b/src/test/regress/expected/mx_application_name.out
@@ -0,0 +1,14 @@
+CREATE SCHEMA mx_app_name;
+CREATE TABLE output (line text);
+-- a hack to run command with another application name
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:xxxxx/regression?application_name=test -c "CREATE TABLE dist_1(a int)"'
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:xxxxx/regression?application_name=test -c "SELECT create_distributed_table(''dist_1'', ''a'');"'
+-- ensure the command executed fine
+SELECT count(*) FROM pg_dist_partition WHERE logicalrelid = 'dist_1'::regclass;
+ count
+---------------------------------------------------------------------
+     1
+(1 row)
+
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:xxxxx/regression?application_name=test -c "DROP TABLE dist_1;"'
+DROP SCHEMA mx_app_name CASCADE;
diff --git a/src/test/regress/multi_mx_schedule b/src/test/regress/multi_mx_schedule
index 973c3bf05..5aaf76aa6 100644
--- a/src/test/regress/multi_mx_schedule
+++ b/src/test/regress/multi_mx_schedule
@@ -59,6 +59,7 @@ test: locally_execute_intermediate_results
 test: multi_mx_alter_distributed_table
 test: update_colocation_mx
 test: resync_metadata_with_sequences
+test: mx_application_name
 
 # should be executed sequentially because it modifies metadata
 test: local_shard_execution_dropped_column
diff --git a/src/test/regress/sql/mx_application_name.sql b/src/test/regress/sql/mx_application_name.sql
new file mode 100644
index 000000000..8e2258774
--- /dev/null
+++ b/src/test/regress/sql/mx_application_name.sql
@@ -0,0 +1,14 @@
+CREATE SCHEMA mx_app_name;
+
+CREATE TABLE output (line text);
+
+-- a hack to run command with another application name
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:57636/regression?application_name=test -c "CREATE TABLE dist_1(a int)"'
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:57636/regression?application_name=test -c "SELECT create_distributed_table(''dist_1'', ''a'');"'
+
+-- ensure the command executed fine
+SELECT count(*) FROM pg_dist_partition WHERE logicalrelid = 'dist_1'::regclass;
+
+\COPY output FROM PROGRAM 'psql postgres://postgres@localhost:57636/regression?application_name=test -c "DROP TABLE dist_1;"'
+
+DROP SCHEMA mx_app_name CASCADE;