ALTER SYSTEM RESET?

*** a/doc/src/sgml/ref/alter_system.sgml
--- b/doc/src/sgml/ref/alter_system.sgml
***************
*** 22,27 **** PostgreSQL documentation
--- 22,28 ----
   <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>
  </synopsis>
   </refsynopsisdiv>
  
***************
*** 30,37 **** 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
!    <literal>DEFAULT</literal>, it removes a configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
--- 31,38 ----
  
    <para>
     <command>ALTER SYSTEM</command> writes the configuration parameter
!    values to the <filename>postgresql.auto.conf</filename> file. Setting the parameter to
!    <literal>DEFAULT</literal>, or using the <command>RESET</command> variant, removes the configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
***************
*** 8486,8491 **** AlterSystemStmt:
--- 8486,8499 ----
  					n->setstmt = $4;
  					$$ = (Node *)n;
  				}
+ 			| ALTER SYSTEM_P RESET var_name
+ 				{
+ 					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+ 					n->setstmt = makeNode(VariableSetStmt);
+ 					n->setstmt->kind = VAR_RESET;
+ 					n->setstmt->name = $4;
+ 					$$ = (Node *)n;
+ 				}
  		;
  
  
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 6720,6725 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
--- 6720,6726 ----
  			break;
  
  		case VAR_SET_DEFAULT:
+ 		case VAR_RESET:
  			value = NULL;
  			break;
  		default:

*** a/doc/src/sgml/ref/alter_system.sgml
--- b/doc/src/sgml/ref/alter_system.sgml
***************
*** 22,27 **** PostgreSQL documentation
--- 22,30 ----
   <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>
  
***************
*** 30,37 **** 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
!    <literal>DEFAULT</literal>, it removes a configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
--- 33,40 ----
  
    <para>
     <command>ALTER SYSTEM</command> writes the configuration parameter
!    values to the <filename>postgresql.auto.conf</filename> file. Setting the parameter to
!    <literal>DEFAULT</literal>, or using the <command>RESET</command> variant, removes the configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
***************
*** 401,407 **** 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 <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
  %type <node>	columnDef columnOptions
--- 401,407 ----
  
  %type <istmt>	insert_rest
  
! %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
***************
*** 1567,1605 **** NonReservedWord_or_Sconst:
  		;
  
  VariableResetStmt:
! 			RESET var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $2;
! 					$$ = (Node *) n;
  				}
! 			| RESET TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = (Node *) n;
  				}
! 			| RESET TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = (Node *) n;
  				}
! 			| RESET SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = (Node *) n;
  				}
! 			| RESET ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = (Node *) n;
  				}
  		;
  
--- 1567,1613 ----
  		;
  
  VariableResetStmt:
! 			RESET reset_rest						{ $$ = (Node *) $2; }
! 		;
! 
! reset_rest:
! 			generic_reset							{ $$ = $1; }
! 			| TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = n;
  				}
! 			| TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = n;
  				}
! 			| SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = n;
  				}
! 		;
! 
! generic_reset:
! 			var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $1;
! 					$$ = n;
  				}
! 			| ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = n;
  				}
  		;
  
***************
*** 8474,8480 **** DropdbStmt: DROP DATABASE database_name
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM SET
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
--- 8482,8488 ----
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
***************
*** 8486,8491 **** AlterSystemStmt:
--- 8494,8505 ----
  					n->setstmt = $4;
  					$$ = (Node *)n;
  				}
+ 			| ALTER SYSTEM_P RESET generic_reset
+ 				{
+ 					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+ 					n->setstmt = $4;
+ 					$$ = (Node *)n;
+ 				}
  		;
  
  
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 6693,6698 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
--- 6693,6699 ----
  {
  	char	   *name;
  	char	   *value;
+ 	bool		resetall = false;
  	int			Tmpfd = -1;
  	FILE	   *infile;
  	struct config_generic *record;
***************
*** 6720,6756 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  			break;
  
  		case VAR_SET_DEFAULT:
  			value = NULL;
  			break;
  		default:
  			elog(ERROR, "unrecognized alter system stmt type: %d",
  				 altersysstmt->setstmt->kind);
  			break;
  	}
  
! 	record = find_option(name, false, LOG);
! 	if (record == NULL)
! 		ereport(ERROR,
! 				(errcode(ERRCODE_UNDEFINED_OBJECT),
! 			   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 	/*
! 	 * Don't allow the parameters which can't be set in configuration
! 	 * files to be set in PG_AUTOCONF_FILENAME file.
! 	 */
! 	if ((record->context == PGC_INTERNAL) ||
! 		(record->flags & GUC_DISALLOW_IN_FILE) ||
! 		(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 		 ereport(ERROR,
! 				 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 				  errmsg("parameter \"%s\" cannot be changed",
! 						 name)));
! 
! 	if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 							  ERROR, true, NULL,
! 							  &newextra))
! 		ereport(ERROR,
! 		(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
  
  
  	/*
--- 6721,6768 ----
  			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,
! 					(errcode(ERRCODE_UNDEFINED_OBJECT),
! 				   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 		/*
! 		 * Don't allow the parameters which can't be set in configuration
! 		 * files to be set in PG_AUTOCONF_FILENAME file.
! 		 */
! 		if ((record->context == PGC_INTERNAL) ||
! 			(record->flags & GUC_DISALLOW_IN_FILE) ||
! 			(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 			 ereport(ERROR,
! 					 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 					  errmsg("parameter \"%s\" cannot be changed",
! 							 name)));
! 	
! 		if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 								  ERROR, true, NULL,
! 								  &newextra))
! 			ereport(ERROR,
! 			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
! 	}
  
  
  	/*
***************
*** 6782,6808 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  
  	PG_TRY();
  	{
! 		if (stat(AutoConfFileName, &st) == 0)
  		{
! 			/* open file PG_AUTOCONF_FILENAME */
! 			infile = AllocateFile(AutoConfFileName, "r");
! 			if (infile == NULL)
! 				ereport(ERROR,
! 						(errmsg("failed to open auto conf file \"%s\": %m ",
! 								AutoConfFileName)));
! 
! 			/* parse it */
! 			ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
! 
! 			FreeFile(infile);
  		}
  
- 		/*
- 		 * replace with new value if the configuration parameter already
- 		 * 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);
  
--- 6794,6828 ----
  
  	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)
! 			{
! 				/* open file PG_AUTOCONF_FILENAME */
! 				infile = AllocateFile(AutoConfFileName, "r");
! 				if (infile == NULL)
! 					ereport(ERROR,
! 							(errmsg("failed to open auto conf file \"%s\": %m ",
! 									AutoConfFileName)));
! 	
! 				/* parse it */
! 				ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
! 	
! 				FreeFile(infile);
! 			}
! 	
! 			/*
! 			 * replace with new value if the configuration parameter already
! 			 * 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);
  

*** a/doc/src/sgml/ref/alter_system.sgml
--- b/doc/src/sgml/ref/alter_system.sgml
***************
*** 22,27 **** PostgreSQL documentation
--- 22,30 ----
   <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>
  
***************
*** 30,37 **** 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
!    <literal>DEFAULT</literal>, it removes a configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
--- 33,41 ----
  
    <para>
     <command>ALTER SYSTEM</command> writes the configuration parameter
!    values to the <filename>postgresql.auto.conf</filename> file.
!    Setting the parameter to <literal>DEFAULT</literal>, or using the
!    <command>RESET</command> variant, removes the configuration entry from
     <filename>postgresql.auto.conf</filename> file. The values will be
     effective after reload of server configuration (SIGHUP) or in next 
     server start based on the type of configuration parameter modified.
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
***************
*** 401,407 **** 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 <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
  %type <node>	columnDef columnOptions
--- 401,407 ----
  
  %type <istmt>	insert_rest
  
! %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
***************
*** 1567,1605 **** NonReservedWord_or_Sconst:
  		;
  
  VariableResetStmt:
! 			RESET var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $2;
! 					$$ = (Node *) n;
  				}
! 			| RESET TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = (Node *) n;
  				}
! 			| RESET TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = (Node *) n;
  				}
! 			| RESET SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = (Node *) n;
  				}
! 			| RESET ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = (Node *) n;
  				}
  		;
  
--- 1567,1613 ----
  		;
  
  VariableResetStmt:
! 			RESET reset_rest						{ $$ = (Node *) $2; }
! 		;
! 
! reset_rest:
! 			generic_reset							{ $$ = $1; }
! 			| TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = n;
  				}
! 			| TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = n;
  				}
! 			| SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = n;
  				}
! 		;
! 
! generic_reset:
! 			var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $1;
! 					$$ = n;
  				}
! 			| ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = n;
  				}
  		;
  
***************
*** 8474,8480 **** DropdbStmt: DROP DATABASE database_name
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM SET
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
--- 8482,8488 ----
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
***************
*** 8486,8491 **** AlterSystemStmt:
--- 8494,8505 ----
  					n->setstmt = $4;
  					$$ = (Node *)n;
  				}
+ 			| ALTER SYSTEM_P RESET generic_reset
+ 				{
+ 					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+ 					n->setstmt = $4;
+ 					$$ = (Node *)n;
+ 				}
  		;
  
  
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 6693,6698 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
--- 6693,6699 ----
  {
  	char	   *name;
  	char	   *value;
+ 	bool		resetall = false;
  	int			Tmpfd = -1;
  	FILE	   *infile;
  	struct config_generic *record;
***************
*** 6720,6756 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  			break;
  
  		case VAR_SET_DEFAULT:
  			value = NULL;
  			break;
  		default:
  			elog(ERROR, "unrecognized alter system stmt type: %d",
  				 altersysstmt->setstmt->kind);
  			break;
  	}
  
! 	record = find_option(name, false, LOG);
! 	if (record == NULL)
! 		ereport(ERROR,
! 				(errcode(ERRCODE_UNDEFINED_OBJECT),
! 			   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 	/*
! 	 * Don't allow the parameters which can't be set in configuration
! 	 * files to be set in PG_AUTOCONF_FILENAME file.
! 	 */
! 	if ((record->context == PGC_INTERNAL) ||
! 		(record->flags & GUC_DISALLOW_IN_FILE) ||
! 		(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 		 ereport(ERROR,
! 				 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 				  errmsg("parameter \"%s\" cannot be changed",
! 						 name)));
! 
! 	if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 							  ERROR, true, NULL,
! 							  &newextra))
! 		ereport(ERROR,
! 		(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
  
  
  	/*
--- 6721,6768 ----
  			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,
! 					(errcode(ERRCODE_UNDEFINED_OBJECT),
! 				   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 		/*
! 		 * Don't allow the parameters which can't be set in configuration
! 		 * files to be set in PG_AUTOCONF_FILENAME file.
! 		 */
! 		if ((record->context == PGC_INTERNAL) ||
! 			(record->flags & GUC_DISALLOW_IN_FILE) ||
! 			(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 			 ereport(ERROR,
! 					 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 					  errmsg("parameter \"%s\" cannot be changed",
! 							 name)));
! 	
! 		if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 								  ERROR, true, NULL,
! 								  &newextra))
! 			ereport(ERROR,
! 			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
! 	}
  
  
  	/*
***************
*** 6782,6808 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  
  	PG_TRY();
  	{
! 		if (stat(AutoConfFileName, &st) == 0)
  		{
! 			/* open file PG_AUTOCONF_FILENAME */
! 			infile = AllocateFile(AutoConfFileName, "r");
! 			if (infile == NULL)
! 				ereport(ERROR,
! 						(errmsg("failed to open auto conf file \"%s\": %m ",
! 								AutoConfFileName)));
! 
! 			/* parse it */
! 			ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
! 
! 			FreeFile(infile);
  		}
  
- 		/*
- 		 * replace with new value if the configuration parameter already
- 		 * 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);
  
--- 6794,6828 ----
  
  	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)
! 			{
! 				/* open file PG_AUTOCONF_FILENAME */
! 				infile = AllocateFile(AutoConfFileName, "r");
! 				if (infile == NULL)
! 					ereport(ERROR,
! 							(errmsg("failed to open auto conf file \"%s\": %m ",
! 									AutoConfFileName)));
! 	
! 				/* parse it */
! 				ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
! 	
! 				FreeFile(infile);
! 			}
! 	
! 			/*
! 			 * replace with new value if the configuration parameter already
! 			 * 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);
  

diff --git a/doc/src/sgml/ref/alter_system.sgml b/doc/src/sgml/ref/alter_system.sgml
index 23c30ef..a6e3210 100644
--- a/doc/src/sgml/ref/alter_system.sgml
+++ b/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
-   <literal>DEFAULT</literal>, it removes a configuration entry from
-   <filename>postgresql.auto.conf</filename> file. The values will be
-   effective after reload of server configuration (SIGHUP) or in next
+   values to the <filename>postgresql.auto.conf</filename> file.
+   Setting the parameter to <literal>DEFAULT</literal>, or using the
+   <command>RESET</command> variant, removes the configuration entry from
+   <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>
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 327f2d2..828c685 100644
--- a/src/backend/parser/gram.y
+++ b/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;
-					$$ = (Node *) n;
+					n->name = "timezone";
+					$$ = n;
 				}
-			| RESET TIME ZONE
+			| TRANSACTION ISOLATION LEVEL
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "timezone";
-					$$ = (Node *) n;
+					n->name = "transaction_isolation";
+					$$ = n;
 				}
-			| RESET TRANSACTION ISOLATION LEVEL
+			| SESSION AUTHORIZATION
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "transaction_isolation";
-					$$ = (Node *) n;
+					n->name = "session_authorization";
+					$$ = n;
 				}
-			| RESET SESSION AUTHORIZATION
+		;
+
+generic_reset:
+			var_name
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "session_authorization";
-					$$ = (Node *) n;
+					n->name = $1;
+					$$ = n;
 				}
-			| RESET ALL
+			| ALL
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET_ALL;
-					$$ = (Node *) n;
+					$$ = n;
 				}
 		;
 
@@ -8485,7 +8494,7 @@ DropdbStmt: DROP DATABASE database_name
 
 /*****************************************************************************
  *
- *		ALTER SYSTEM SET
+ *		ALTER SYSTEM
  *
  * This is used to change configuration parameters persistently.
  *****************************************************************************/
@@ -8497,6 +8506,12 @@ AlterSystemStmt:
 					n->setstmt = $4;
 					$$ = (Node *)n;
 				}
+			| ALTER SYSTEM_P RESET generic_reset
+				{
+					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+					n->setstmt = $4;
+					$$ = (Node *)n;
+				}
 		;
 
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index a8a17c2..ce1c969 100644
--- a/src/backend/utils/misc/guc.c
+++ b/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;
@@ -6737,37 +6740,48 @@ 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;
 	}
 
-	record = find_option(name, false, LOG);
-	if (record == NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_UNDEFINED_OBJECT),
-			   errmsg("unrecognized configuration parameter \"%s\"", name)));
+	/* 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,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+				   errmsg("unrecognized configuration parameter \"%s\"", name)));
 
-	/*
-	 * Don't allow the parameters which can't be set in configuration
-	 * files to be set in PG_AUTOCONF_FILENAME file.
-	 */
-	if ((record->context == PGC_INTERNAL) ||
-		(record->flags & GUC_DISALLOW_IN_FILE) ||
-		(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
-		 ereport(ERROR,
-				 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
-				  errmsg("parameter \"%s\" cannot be changed",
-						 name)));
-
-	if (!validate_conf_option(record, name, value, PGC_S_FILE,
-							  ERROR, true, NULL,
-							  &newextra))
-		ereport(ERROR,
-		(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
+		/*
+		 * Don't allow the parameters which can't be set in configuration
+		 * files to be set in PG_AUTOCONF_FILENAME file.
+		 */
+		if ((record->context == PGC_INTERNAL) ||
+			(record->flags & GUC_DISALLOW_IN_FILE) ||
+			(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
+			 ereport(ERROR,
+					 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
+					  errmsg("parameter \"%s\" cannot be changed",
+							 name)));
+
+		if (!validate_conf_option(record, name, value, PGC_S_FILE,
+								  ERROR, true, NULL,
+								  &newextra))
+			ereport(ERROR,
+			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
+	}
 
 
 	/*
@@ -6799,26 +6813,34 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 
 	PG_TRY();
 	{
-		if (stat(AutoConfFileName, &st) == 0)
+		/*
+		 * 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)
 		{
-			/* open file PG_AUTOCONF_FILENAME */
-			infile = AllocateFile(AutoConfFileName, "r");
-			if (infile == NULL)
-				ereport(ERROR,
-						(errmsg("failed to open auto conf file \"%s\": %m ",
-								AutoConfFileName)));
+			if (stat(AutoConfFileName, &st) == 0)
+			{
+				/* open file PG_AUTOCONF_FILENAME */
+				infile = AllocateFile(AutoConfFileName, "r");
+				if (infile == NULL)
+					ereport(ERROR,
+							(errmsg("failed to open auto conf file \"%s\": %m ",
+									AutoConfFileName)));
 
-			/* parse it */
-			ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
+				/* parse it */
+				ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
 
-			FreeFile(infile);
-		}
+				FreeFile(infile);
+			}
 
-		/*
-		 * replace with new value if the configuration parameter already
-		 * exists OR add it as a new cofiguration parameter in the file.
-		 */
-		replace_auto_config_value(&head, &tail, AutoConfFileName, name, value);
+			/*
+			 * replace with new value if the configuration parameter already
+			 * 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);

diff --git a/doc/src/sgml/ref/alter_system.sgml b/doc/src/sgml/ref/alter_system.sgml
index 23c30ef..a6e3210 100644
--- a/doc/src/sgml/ref/alter_system.sgml
+++ b/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
-   <literal>DEFAULT</literal>, it removes a configuration entry from
-   <filename>postgresql.auto.conf</filename> file. The values will be
-   effective after reload of server configuration (SIGHUP) or in next
+   values to the <filename>postgresql.auto.conf</filename> file.
+   Setting the parameter to <literal>DEFAULT</literal>, or using the
+   <command>RESET</command> variant, removes the configuration entry from
+   <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>
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 6f4d645..b46dd7b 100644
--- a/src/backend/parser/gram.y
+++ b/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;
-					$$ = (Node *) n;
+					n->name = "timezone";
+					$$ = n;
 				}
-			| RESET TIME ZONE
+			| TRANSACTION ISOLATION LEVEL
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "timezone";
-					$$ = (Node *) n;
+					n->name = "transaction_isolation";
+					$$ = n;
 				}
-			| RESET TRANSACTION ISOLATION LEVEL
+			| SESSION AUTHORIZATION
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "transaction_isolation";
-					$$ = (Node *) n;
+					n->name = "session_authorization";
+					$$ = n;
 				}
-			| RESET SESSION AUTHORIZATION
+		;
+
+generic_reset:
+			var_name
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
 					n->kind = VAR_RESET;
-					n->name = "session_authorization";
-					$$ = (Node *) n;
+					n->name = $1;
+					$$ = 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;
+				}
 		;
 
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 8c57803..af667f5 100644
--- a/src/backend/utils/misc/guc.c
+++ b/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;
@@ -6737,37 +6740,48 @@ 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;
 	}
 
-	record = find_option(name, false, LOG);
-	if (record == NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_UNDEFINED_OBJECT),
-			   errmsg("unrecognized configuration parameter \"%s\"", name)));
+	/* 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,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+				   errmsg("unrecognized configuration parameter \"%s\"", name)));
 
-	/*
-	 * Don't allow the parameters which can't be set in configuration
-	 * files to be set in PG_AUTOCONF_FILENAME file.
-	 */
-	if ((record->context == PGC_INTERNAL) ||
-		(record->flags & GUC_DISALLOW_IN_FILE) ||
-		(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
-		 ereport(ERROR,
-				 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
-				  errmsg("parameter \"%s\" cannot be changed",
-						 name)));
-
-	if (!validate_conf_option(record, name, value, PGC_S_FILE,
-							  ERROR, true, NULL,
-							  &newextra))
-		ereport(ERROR,
-		(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
+		/*
+		 * Don't allow the parameters which can't be set in configuration
+		 * files to be set in PG_AUTOCONF_FILENAME file.
+		 */
+		if ((record->context == PGC_INTERNAL) ||
+			(record->flags & GUC_DISALLOW_IN_FILE) ||
+			(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
+			 ereport(ERROR,
+					 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
+					  errmsg("parameter \"%s\" cannot be changed",
+							 name)));
+
+		if (!validate_conf_option(record, name, value, PGC_S_FILE,
+								  ERROR, true, NULL,
+								  &newextra))
+			ereport(ERROR,
+			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
+	}
 
 
 	/*
@@ -6799,26 +6813,34 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 
 	PG_TRY();
 	{
-		if (stat(AutoConfFileName, &st) == 0)
+		/*
+		 * 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)
 		{
-			/* open file PG_AUTOCONF_FILENAME */
-			infile = AllocateFile(AutoConfFileName, "r");
-			if (infile == NULL)
-				ereport(ERROR,
-						(errmsg("failed to open auto conf file \"%s\": %m ",
-								AutoConfFileName)));
+			if (stat(AutoConfFileName, &st) == 0)
+			{
+				/* open file PG_AUTOCONF_FILENAME */
+				infile = AllocateFile(AutoConfFileName, "r");
+				if (infile == NULL)
+					ereport(ERROR,
+							(errmsg("failed to open auto conf file \"%s\": %m ",
+									AutoConfFileName)));
 
-			/* parse it */
-			ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
+				/* parse it */
+				ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
 
-			FreeFile(infile);
-		}
+				FreeFile(infile);
+			}
 
-		/*
-		 * replace with new value if the configuration parameter already
-		 * exists OR add it as a new cofiguration parameter in the file.
-		 */
-		replace_auto_config_value(&head, &tail, AutoConfFileName, name, value);
+			/*
+			 * replace with new value if the configuration parameter already
+			 * 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);
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 76b2b04..cc9c884 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -963,7 +963,7 @@ 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 +1328,20 @@ 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 &&

*** a/doc/src/sgml/ref/alter_system.sgml
--- b/doc/src/sgml/ref/alter_system.sgml
***************
*** 22,27 **** PostgreSQL documentation
--- 22,30 ----
   <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>
  
***************
*** 30,39 **** 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
!    <literal>DEFAULT</literal>, it removes a configuration entry from
!    <filename>postgresql.auto.conf</filename> file. 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>
  
--- 33,44 ----
  
    <para>
     <command>ALTER SYSTEM</command> writes the configuration parameter
!    values to the <filename>postgresql.auto.conf</filename> file.
!    Setting the parameter to <literal>DEFAULT</literal>, or using the
!    <command>RESET</command> variant, removes the configuration entry from
!    <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>
  
*** a/src/backend/parser/gram.y
--- b/src/backend/parser/gram.y
***************
*** 411,417 **** 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 <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
  %type <node>	columnDef columnOptions
--- 411,418 ----
  
  %type <istmt>	insert_rest
  
! %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
***************
*** 1579,1617 **** NonReservedWord_or_Sconst:
  		;
  
  VariableResetStmt:
! 			RESET var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $2;
! 					$$ = (Node *) n;
  				}
! 			| RESET TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = (Node *) n;
  				}
! 			| RESET TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = (Node *) n;
  				}
! 			| RESET SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = (Node *) n;
  				}
! 			| RESET ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = (Node *) n;
  				}
  		;
  
--- 1580,1626 ----
  		;
  
  VariableResetStmt:
! 			RESET reset_rest						{ $$ = (Node *) $2; }
! 		;
! 
! reset_rest:
! 			generic_reset							{ $$ = $1; }
! 			| TIME ZONE
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "timezone";
! 					$$ = n;
  				}
! 			| TRANSACTION ISOLATION LEVEL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "transaction_isolation";
! 					$$ = n;
  				}
! 			| SESSION AUTHORIZATION
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = "session_authorization";
! 					$$ = n;
  				}
! 		;
! 
! generic_reset:
! 			var_name
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET;
! 					n->name = $1;
! 					$$ = n;
  				}
! 			| ALL
  				{
  					VariableSetStmt *n = makeNode(VariableSetStmt);
  					n->kind = VAR_RESET_ALL;
! 					$$ = n;
  				}
  		;
  
***************
*** 8494,8500 **** DropdbStmt: DROP DATABASE database_name
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM SET
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
--- 8503,8509 ----
  
  /*****************************************************************************
   *
!  *		ALTER SYSTEM
   *
   * This is used to change configuration parameters persistently.
   *****************************************************************************/
***************
*** 8506,8511 **** AlterSystemStmt:
--- 8515,8526 ----
  					n->setstmt = $4;
  					$$ = (Node *)n;
  				}
+ 			| ALTER SYSTEM_P RESET generic_reset
+ 				{
+ 					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+ 					n->setstmt = $4;
+ 					$$ = (Node *)n;
+ 				}
  		;
  
  
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 6696,6701 **** replace_auto_config_value(ConfigVariable **head_p, ConfigVariable **tail_p,
--- 6696,6703 ----
   * 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.
***************
*** 6710,6715 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
--- 6712,6718 ----
  {
  	char	   *name;
  	char	   *value;
+ 	bool		resetall = false;
  	int			Tmpfd = -1;
  	FILE	   *infile;
  	struct config_generic *record;
***************
*** 6737,6773 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  			break;
  
  		case VAR_SET_DEFAULT:
  			value = NULL;
  			break;
  		default:
  			elog(ERROR, "unrecognized alter system stmt type: %d",
  				 altersysstmt->setstmt->kind);
  			break;
  	}
  
! 	record = find_option(name, false, LOG);
! 	if (record == NULL)
! 		ereport(ERROR,
! 				(errcode(ERRCODE_UNDEFINED_OBJECT),
! 			   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 	/*
! 	 * Don't allow the parameters which can't be set in configuration
! 	 * files to be set in PG_AUTOCONF_FILENAME file.
! 	 */
! 	if ((record->context == PGC_INTERNAL) ||
! 		(record->flags & GUC_DISALLOW_IN_FILE) ||
! 		(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 		 ereport(ERROR,
! 				 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 				  errmsg("parameter \"%s\" cannot be changed",
! 						 name)));
! 
! 	if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 							  ERROR, true, NULL,
! 							  &newextra))
! 		ereport(ERROR,
! 		(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
  
  
  	/*
--- 6740,6787 ----
  			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,
! 					(errcode(ERRCODE_UNDEFINED_OBJECT),
! 				   errmsg("unrecognized configuration parameter \"%s\"", name)));
  
! 		/*
! 		 * Don't allow the parameters which can't be set in configuration
! 		 * files to be set in PG_AUTOCONF_FILENAME file.
! 		 */
! 		if ((record->context == PGC_INTERNAL) ||
! 			(record->flags & GUC_DISALLOW_IN_FILE) ||
! 			(record->flags & GUC_DISALLOW_IN_AUTO_FILE))
! 			 ereport(ERROR,
! 					 (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
! 					  errmsg("parameter \"%s\" cannot be changed",
! 							 name)));
! 
! 		if (!validate_conf_option(record, name, value, PGC_S_FILE,
! 								  ERROR, true, NULL,
! 								  &newextra))
! 			ereport(ERROR,
! 			(errmsg("invalid value for parameter \"%s\": \"%s\"", name, value)));
! 	}
  
  
  	/*
***************
*** 6799,6824 **** AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
  
  	PG_TRY();
  	{
! 		if (stat(AutoConfFileName, &st) == 0)
  		{
! 			/* open file PG_AUTOCONF_FILENAME */
! 			infile = AllocateFile(AutoConfFileName, "r");
! 			if (infile == NULL)
! 				ereport(ERROR,
! 						(errmsg("failed to open auto conf file \"%s\": %m ",
! 								AutoConfFileName)));
  
! 			/* parse it */
! 			ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
  
! 			FreeFile(infile);
! 		}
  
! 		/*
! 		 * replace with new value if the configuration parameter already
! 		 * 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);
--- 6813,6846 ----
  
  	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)
! 			{
! 				/* open file PG_AUTOCONF_FILENAME */
! 				infile = AllocateFile(AutoConfFileName, "r");
! 				if (infile == NULL)
! 					ereport(ERROR,
! 							(errmsg("failed to open auto conf file \"%s\": %m ",
! 									AutoConfFileName)));
  
! 				/* parse it */
! 				ParseConfigFp(infile, AutoConfFileName, 0, LOG, &head, &tail);
  
! 				FreeFile(infile);
! 			}
  
! 			/*
! 			 * replace with new value if the configuration parameter already
! 			 * 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);
*** a/src/bin/psql/tab-complete.c
--- b/src/bin/psql/tab-complete.c
***************
*** 545,551 **** 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'"
  
  #define Query_for_list_of_set_vars \
  "SELECT name FROM "\
--- 545,552 ----
  "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'"\
! " UNION ALL SELECT 'all' ss"
  
  #define Query_for_list_of_set_vars \
  "SELECT name FROM "\
***************
*** 963,969 **** 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",
  			"TABLESPACE", "TEXT SEARCH", "TRIGGER", "TYPE",
  		"USER", "USER MAPPING FOR", "VIEW", NULL};
  
--- 964,970 ----
  		{"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", "TABLE",
  			"TABLESPACE", "TEXT SEARCH", "TRIGGER", "TYPE",
  		"USER", "USER MAPPING FOR", "VIEW", NULL};
  
***************
*** 1328,1337 **** psql_completion(const char *text, int start, int end)
  
  		COMPLETE_WITH_LIST(list_ALTER_SERVER);
  	}
! 	/* ALTER SYSTEM SET <name> */
  	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&
  			 pg_strcasecmp(prev2_wd, "SYSTEM") == 0 &&
! 			 pg_strcasecmp(prev_wd, "SET") == 0)
  		COMPLETE_WITH_QUERY(Query_for_list_of_alter_system_set_vars);
  	/* ALTER VIEW <name> */
  	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&
--- 1329,1348 ----
  
  		COMPLETE_WITH_LIST(list_ALTER_SERVER);
  	}
! 	/* 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, "RESET") == 0))
  		COMPLETE_WITH_QUERY(Query_for_list_of_alter_system_set_vars);
  	/* ALTER VIEW <name> */
  	else if (pg_strcasecmp(prev3_wd, "ALTER") == 0 &&