Support ALTER SYSTEM RESET command.

This patch allows us to execute ALTER SYSTEM RESET command to
remove the configuration entry from postgresql.auto.conf.

Vik Fearing, reviewed by Amit Kapila and me.

doc/src/sgml/ref/alter_system.sgml

@@ -22,6 +22,9 @@ PostgreSQL documentation
  <refsynopsisdiv>
 <synopsis>
 ALTER SYSTEM SET <replaceable class="PARAMETER">configuration_parameter</replaceable> { TO | = } { <replaceable class="PARAMETER">value</replaceable> | '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
+
+ALTER SYSTEM RESET <replaceable class="PARAMETER">configuration_parameter</replaceable>
+ALTER SYSTEM RESET ALL
 </synopsis>
  </refsynopsisdiv>
 
@@ -30,10 +33,12 @@ ALTER SYSTEM SET <replaceable class="PARAMETER">configuration_parameter</replace
 
   <para>
    <command>ALTER SYSTEM</command> writes the configuration parameter
-   values to the <filename>postgresql.auto.conf</filename> file. With
+   values to the <filename>postgresql.auto.conf</filename> file.
-   <literal>DEFAULT</literal>, it removes a configuration entry from
+   Setting the parameter to <literal>DEFAULT</literal>, or using the
-   <filename>postgresql.auto.conf</filename> file. The values will be
+   <command>RESET</command> variant, removes the configuration entry from
-   effective after reload of server configuration (SIGHUP) or in next
+   <filename>postgresql.auto.conf</filename> file. Use <literal>RESET
+   ALL</literal> to clear all configuration entries.  The values will
+   be effective after reload of server configuration (SIGHUP) or in next
    server start based on the type of configuration parameter modified.
   </para>
 

src/backend/parser/gram.y

@@ -411,7 +411,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 %type <istmt>	insert_rest
 
-%type <vsetstmt> generic_set set_rest set_rest_more SetResetClause FunctionSetResetClause
+%type <vsetstmt> generic_set set_rest set_rest_more generic_reset reset_rest
+				 SetResetClause FunctionSetResetClause
 
 %type <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
 %type <node>	columnDef columnOptions
@@ -1579,39 +1580,47 @@ NonReservedWord_or_Sconst:
 		;
 
 VariableResetStmt:
-			RESET var_name
+			RESET reset_rest						{ $$ = (Node *) $2; }
+		;
+
+reset_rest:
+			generic_reset							{ $$ = $1; }
+			| TIME ZONE
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = $2;
+					n->name = "timezone";
-					$$ = (Node *) n;
+					$$ = n;
 				}
-			| RESET TIME ZONE
+			| TRANSACTION ISOLATION LEVEL
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "timezone";
+					n->name = "transaction_isolation";
-					$$ = (Node *) n;
+					$$ = n;
 				}
-			| RESET TRANSACTION ISOLATION LEVEL
+			| SESSION AUTHORIZATION
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "transaction_isolation";
+					n->name = "session_authorization";
-					$$ = (Node *) n;
+					$$ = n;
 				}
-			| RESET SESSION AUTHORIZATION
+		;
+
+generic_reset:
+			var_name
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "session_authorization";
+					n->name = $1;
-					$$ = (Node *) n;
+					$$ = n;
 				}
-			| RESET ALL
+			| ALL
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET_ALL;
-					$$ = (Node *) n;
+					$$ = n;
 				}
 		;
 
@@ -8494,7 +8503,7 @@ DropdbStmt: DROP DATABASE database_name
 
 /*****************************************************************************
  *
- *		ALTER SYSTEM SET
+ *		ALTER SYSTEM
  *
  * This is used to change configuration parameters persistently.
  *****************************************************************************/
@@ -8506,6 +8515,12 @@ AlterSystemStmt:
 					n->setstmt = $4;
 					$$ = (Node *)n;
 				}
+			| ALTER SYSTEM_P RESET generic_reset
+				{
+					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+					n->setstmt = $4;
+					$$ = (Node *)n;
+				}
 		;
 
 

src/backend/utils/misc/guc.c

@@ -6696,6 +6696,8 @@ replace_auto_config_value(ConfigVariable **head_p, ConfigVariable **tail_p,
  * This function takes all previous configuration parameters
  * set by ALTER SYSTEM command and the currently set ones
  * and write them all to the automatic configuration file.
+ * It just writes an empty file incase user wants to reset
+ * all the parameters.
  *
  * The configuration parameters are written to a temporary
  * file then renamed to the final name.
@@ -6710,6 +6712,7 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 {
 	char	   *name;
 	char	   *value;
+	bool		resetall = false;
 	int			Tmpfd = -1;
 	FILE	   *infile;
 	struct config_generic *record;
@@ -6737,14 +6740,24 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 			break;
 
 		case VAR_SET_DEFAULT:
+		case VAR_RESET:
+			value = NULL;
+			break;
+
+		case VAR_RESET_ALL:
 			value = NULL;
+			resetall = true;
 			break;
+
 		default:
 			elog(ERROR, "unrecognized alter system stmt type: %d",
 				 altersysstmt->setstmt->kind);
 			break;
 	}
 
+	/* If we're resetting everything, there's no need to validate anything */
+	if (!resetall)
+	{
 		record = find_option(name, false, LOG);
 		if (record == NULL)
 			ereport(ERROR,
@@ -6768,6 +6781,7 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 								  &newextra))
 			ereport(ERROR,
 			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
+	}
 
 
 	/*
@@ -6798,6 +6812,13 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 						AutoConfTmpFileName)));
 
 	PG_TRY();
+	{
+		/*
+		 * If we're going to reset everything, then don't open the file, don't
+		 * parse it, and don't do anything with the configuration list.  Just
+		 * write out an empty file.
+		 */
+		if (!resetall)
 		{
 			if (stat(AutoConfFileName, &st) == 0)
 			{
@@ -6819,6 +6840,7 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 			 * exists OR add it as a new cofiguration parameter in the file.
 			 */
 			replace_auto_config_value(&head, &tail, AutoConfFileName, name, value);
+		}
 
 		/* Write and sync the new contents to the temporary file */
 		write_auto_conf_file(Tmpfd, AutoConfTmpFileName, &head);

src/bin/psql/tab-complete.c

@@ -545,7 +545,8 @@ static const SchemaQuery Query_for_list_of_matviews = {
 "SELECT name FROM "\
 " (SELECT pg_catalog.lower(name) AS name FROM pg_catalog.pg_settings "\
 "  WHERE context != 'internal') ss "\
-" WHERE substring(name,1,%d)='%s'"
+" WHERE substring(name,1,%d)='%s'"\
+" UNION ALL SELECT 'all' ss"
 
 #define Query_for_list_of_set_vars \
 "SELECT name FROM "\
@@ -963,7 +964,7 @@ psql_completion(const char *text, int start, int end)
 		{"AGGREGATE", "COLLATION", "CONVERSION", "DATABASE", "DEFAULT PRIVILEGES", "DOMAIN",
 			"EVENT TRIGGER", "EXTENSION", "FOREIGN DATA WRAPPER", "FOREIGN TABLE", "FUNCTION",
 			"GROUP", "INDEX", "LANGUAGE", "LARGE OBJECT", "MATERIALIZED VIEW", "OPERATOR",
-			"ROLE", "RULE", "SCHEMA", "SERVER", "SEQUENCE", "SYSTEM SET", "TABLE",
+			"ROLE", "RULE", "SCHEMA", "SERVER", "SEQUENCE", "SYSTEM", "TABLE",
 			"TABLESPACE", "TEXT SEARCH", "TRIGGER", "TYPE",
 		"USER", "USER MAPPING FOR", "VIEW", NULL};
 
@@ -1328,10 +1329,20 @@ psql_completion(const char *text, int start, int end)
 
 		COMPLETE_WITH_LIST(list_ALTER_SERVER);
 	}
-	/* ALTER SYSTEM SET <name> */
+	/* ALTER SYSTEM SET, RESET, RESET ALL */
+	else if (pg_strcasecmp(prev2_wd, "ALTER") == 0 &&
+			 pg_strcasecmp(prev_wd, "SYSTEM") == 0)
+	{
+		static const char *const list_ALTERSYSTEM[] =
+		{"SET", "RESET", NULL};
+
+		COMPLETE_WITH_LIST(list_ALTERSYSTEM);
+	}
+	/* ALTER SYSTEM SET|RESET <name> */
 	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&
 			 pg_strcasecmp(prev2_wd, "SYSTEM") == 0 &&
-			 pg_strcasecmp(prev_wd, "SET") == 0)
+			 (pg_strcasecmp(prev_wd, "SET") == 0 ||
+			 pg_strcasecmp(prev_wd, "RESET") == 0))
 		COMPLETE_WITH_QUERY(Query_for_list_of_alter_system_set_vars);
 	/* ALTER VIEW <name> */
 	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&