guc_no_reset_v2.patch

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 8a802fb225..0d604e1a83 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -23881,6 +23881,10 @@ SELECT currval(pg_get_serial_sequence('sometable', 'id'));
           <literal>NO_SHOW_ALL</literal>: parameters excluded from
           <command>SHOW ALL</command> commands.
          </member>
+         <member>
+          <literal>NO_RESET</literal>: parameters do not support
+          <command>RESET</command> commands.
+         </member>
          <member>
           <literal>NO_RESET_ALL</literal>: parameters excluded from
           <command>RESET ALL</command> commands.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index e7f0a380e6..6e93f97cd7 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1709,7 +1709,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's read-only status."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactReadOnly,
 		false,
@@ -1728,7 +1728,7 @@ static struct config_bool ConfigureNamesBool[] =
 		{"transaction_deferrable", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Whether to defer a read-only serializable transaction until it can be executed with no possible serialization failures."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactDeferrable,
 		false,
@@ -4752,7 +4752,7 @@ static struct config_enum ConfigureNamesEnum[] =
 		{"transaction_isolation", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the current transaction's isolation level."),
 			NULL,
-			GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
 		&XactIsoLevel,
 		XACT_READ_COMMITTED, isolation_level_options,
@@ -7599,6 +7599,16 @@ set_config_option(const char *name, const char *value,
 		}
 	}
 
+	/* Check if the parameter supports RESET */
+	if (record->flags & GUC_NO_RESET && value == NULL)
+	{
+		ereport(elevel,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("parameter \"%s\" cannot be reset",
+						name)));
+		return 0;
+	}
+
 	/*
 	 * Should we set reset/stacked values?	(If so, the behavior is not
 	 * transactional.)	This is done either when we get a default value from
@@ -9706,7 +9716,7 @@ GetConfigOptionByName(const char *name, const char **varname, bool missing_ok)
 Datum
 pg_settings_get_flags(PG_FUNCTION_ARGS)
 {
-#define MAX_GUC_FLAGS	5
+#define MAX_GUC_FLAGS	6
 	char	   *varname = TextDatumGetCString(PG_GETARG_DATUM(0));
 	struct config_generic *record;
 	int			cnt = 0;
@@ -9721,6 +9731,8 @@ pg_settings_get_flags(PG_FUNCTION_ARGS)
 
 	if (record->flags & GUC_EXPLAIN)
 		flags[cnt++] = CStringGetTextDatum("EXPLAIN");
+	if (record->flags & GUC_NO_RESET)
+		flags[cnt++] = CStringGetTextDatum("NO_RESET");
 	if (record->flags & GUC_NO_RESET_ALL)
 		flags[cnt++] = CStringGetTextDatum("NO_RESET_ALL");
 	if (record->flags & GUC_NO_SHOW_ALL)
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index ea774968f0..ecbcf3a8c9 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -235,6 +235,8 @@ typedef enum
  */
 #define GUC_RUNTIME_COMPUTED  0x200000
 
+#define GUC_NO_RESET		  0x400000	/* ignore when RESET */
+
 #define GUC_UNIT				(GUC_UNIT_MEMORY | GUC_UNIT_TIME)
 
 
diff --git a/src/test/regress/expected/guc.out b/src/test/regress/expected/guc.out
index 3de6404ba5..801d84bd39 100644
--- a/src/test/regress/expected/guc.out
+++ b/src/test/regress/expected/guc.out
@@ -839,6 +839,7 @@ SELECT pg_settings_get_flags('does_not_exist');
 
 CREATE TABLE tab_settings_flags AS SELECT name, category,
     'EXPLAIN'          = ANY(flags) AS explain,
+    'NO_RESET'         = ANY(flags) AS no_reset,
     'NO_RESET_ALL'     = ANY(flags) AS no_reset_all,
     'NO_SHOW_ALL'      = ANY(flags) AS no_show_all,
     'NOT_IN_SAMPLE'    = ANY(flags) AS not_in_sample,
diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index 599d511a67..2b5bc9d4c1 100644
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -44,6 +44,37 @@ SELECT * FROM xacttest;
  777 | 777.777
 (5 rows)
 
+-- Test that transaction characteristics cannot reset.
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+SELECT count(*) FROM xacttest;
+ count 
+-------
+     5
+(1 row)
+
+RESET transaction_isolation; -- error
+ERROR:  parameter "transaction_isolation" cannot be reset
+END;
+BEGIN TRANSACTION READ ONLY;
+SELECT count(*) FROM xacttest;
+ count 
+-------
+     5
+(1 row)
+
+RESET transaction_read_only; -- error
+ERROR:  parameter "transaction_read_only" cannot be reset
+END;
+BEGIN TRANSACTION DEFERRABLE;
+SELECT count(*) FROM xacttest;
+ count 
+-------
+     5
+(1 row)
+
+RESET transaction_deferrable; -- error
+ERROR:  parameter "transaction_deferrable" cannot be reset
+END;
 -- Read-only tests
 CREATE TABLE writetest (a int);
 CREATE TEMPORARY TABLE temptest (a int);
diff --git a/src/test/regress/sql/guc.sql b/src/test/regress/sql/guc.sql
index d5db101e48..c8b612b5d5 100644
--- a/src/test/regress/sql/guc.sql
+++ b/src/test/regress/sql/guc.sql
@@ -324,6 +324,7 @@ SELECT pg_settings_get_flags(NULL);
 SELECT pg_settings_get_flags('does_not_exist');
 CREATE TABLE tab_settings_flags AS SELECT name, category,
     'EXPLAIN'          = ANY(flags) AS explain,
+    'NO_RESET'         = ANY(flags) AS no_reset,
     'NO_RESET_ALL'     = ANY(flags) AS no_reset_all,
     'NO_SHOW_ALL'      = ANY(flags) AS no_show_all,
     'NOT_IN_SAMPLE'    = ANY(flags) AS not_in_sample,
diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index 0a716b506b..5601ba31aa 100644
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -35,6 +35,21 @@ SELECT oid FROM pg_class WHERE relname = 'disappear';
 -- should have members again
 SELECT * FROM xacttest;
 
+-- Test that transaction characteristics cannot reset.
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+SELECT count(*) FROM xacttest;
+RESET transaction_isolation; -- error
+END;
+
+BEGIN TRANSACTION READ ONLY;
+SELECT count(*) FROM xacttest;
+RESET transaction_read_only; -- error
+END;
+
+BEGIN TRANSACTION DEFERRABLE;
+SELECT count(*) FROM xacttest;
+RESET transaction_deferrable; -- error
+END;
 
 -- Read-only tests