Add ALTER SYSTEM command to edit the server configuration file.

Patch contributed by Amit Kapila. Reviewed by Hari Babu, Masao Fujii,
Boszormenyi Zoltan, Andres Freund, Greg Smith and others.

doc/src/sgml/config.sgml

@@ -158,6 +158,19 @@ SET ENABLE_SEQSCAN TO OFF;
      require superuser permission to change via <command>SET</command> or
      <command>ALTER</>.
     </para>
+
+    <para>
+     Another way to change configuration parameters persistently is by
+     use of <xref linkend="SQL-ALTERSYSTEM">
+     command, for example:
+<screen>
+ALTER SYSTEM SET checkpoint_timeout TO 600;
+</screen>
+     This command will allow users to change values persistently
+     through SQL command. The values will be effective after reload of server configuration
+     (<acronym>SIGHUP</>) or server startup. The effect of this command is similar to when
+     user manually changes values in <filename>postgresql.conf</filename>.
+    </para>
    </sect2>
 
    <sect2 id="config-setting-examining">

doc/src/sgml/ref/allfiles.sgml

@@ -30,6 +30,7 @@ Complete list of usable sgml source files in this directory.
 <!ENTITY alterSchema        SYSTEM "alter_schema.sgml">
 <!ENTITY alterServer        SYSTEM "alter_server.sgml">
 <!ENTITY alterSequence      SYSTEM "alter_sequence.sgml">
+<!ENTITY alterSystem        SYSTEM "alter_system.sgml">
 <!ENTITY alterTable         SYSTEM "alter_table.sgml">
 <!ENTITY alterTableSpace    SYSTEM "alter_tablespace.sgml">
 <!ENTITY alterTSConfig      SYSTEM "alter_tsconfig.sgml">

doc/src/sgml/ref/alter_system.sgml

+<!--
+doc/src/sgml/ref/alter_system.sgml
+PostgreSQL documentation
+-->
+
+<refentry id="SQL-ALTERSYSTEM">
+ <refmeta>
+  <refentrytitle>ALTER SYSTEM</refentrytitle>
+  <manvolnum>7</manvolnum>
+  <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>ALTER SYSTEM</refname>
+  <refpurpose>change a server configuration parameter</refpurpose>
+ </refnamediv>
+
+ <indexterm zone="sql-altersystem">
+  <primary>ALTER SYSTEM</primary>
+ </indexterm>
+
+ <refsynopsisdiv>
+<synopsis>
+ALTER SYSTEM SET <replaceable class="PARAMETER">configuration_parameter</replaceable> { TO | = } { <replaceable class="PARAMETER">value</replaceable> | '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <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>
+
+  <para>
+   This command is not allowed inside transaction block or function.
+  </para>
+  
+  <para>
+   See <xref linkend="config-setting"> for other ways to set the parameters and 
+   how they become effective.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Parameters</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><replaceable class="parameter">configuration_parameter</replaceable></term>
+    <listitem>
+     <para>
+      Name of a settable run-time parameter.  Available parameters are
+      documented in <xref linkend="runtime-config">.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">value</replaceable></term>
+    <listitem>
+     <para>
+      New value of parameter.  Values can be specified as string
+      constants, identifiers, numbers, or comma-separated lists of
+      these, as appropriate for the particular parameter.
+      <literal>DEFAULT</literal> can be written to specify to remove the
+      parameter and its value from <filename>postgresql.auto.conf</filename>
+     </para>
+    </listitem>
+   </varlistentry>
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Examples</title>
+
+  <para>
+   Set the <literal>wal_level</>:
+<programlisting>
+ALTER SYSTEM SET wal_level = hot_standby;
+</programlisting>
+  </para>
+
+  <para>
+   Set the <literal>authentication_timeout</>:
+<programlisting>
+ALTER SYSTEM SET authentication_timeout = 10;
+</programlisting></para>
+ </refsect1>
+
+ <refsect1>
+  <title>Compatibility</title>
+
+  <para>
+   The <command>ALTER SYSTEM</command> statement is a
+   <productname>PostgreSQL</productname> extension.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>See Also</title>
+
+  <simplelist type="inline">
+   <member><xref linkend="SQL-SET"></member>
+   <member><xref linkend="SQL-SHOW"></member>
+  </simplelist>
+ </refsect1>
+
+</refentry>

doc/src/sgml/reference.sgml

@@ -58,6 +58,7 @@
    &alterSchema;
    &alterSequence;
    &alterServer;
+   &alterSystem;
    &alterTable;
    &alterTableSpace;
    &alterTSConfig;

doc/src/sgml/storage.sgml

@@ -125,6 +125,12 @@ Item
  <entry>Subdirectory containing WAL (Write Ahead Log) files</entry>
 </row>
 
+<row>
+ <entry><filename>postgresql.auto.conf</></entry>
+ <entry>A file used for storing configuration parameters that are set by
+<command>ALTER SYSTEM</command></entry>
+</row>
+
 <row>
  <entry><filename>postmaster.opts</></entry>
  <entry>A file recording the command-line options the server was

src/backend/nodes/copyfuncs.c

@@ -3292,6 +3292,16 @@ _copyReplicaIdentityStmt(const ReplicaIdentityStmt *from)
 	return newnode;
 }
 
+static AlterSystemStmt *
+_copyAlterSystemStmt(const AlterSystemStmt * from)
+{
+	AlterSystemStmt *newnode = makeNode(AlterSystemStmt);
+
+	COPY_NODE_FIELD(setstmt);
+
+	return newnode;
+}
+
 static CreateSeqStmt *
 _copyCreateSeqStmt(const CreateSeqStmt *from)
 {
@@ -4368,6 +4378,9 @@ copyObject(const void *from)
 		case T_ReplicaIdentityStmt:
 			retval = _copyReplicaIdentityStmt(from);
 			break;
+		case T_AlterSystemStmt:
+			retval = _copyAlterSystemStmt(from);
+			break;
 		case T_CreateSeqStmt:
 			retval = _copyCreateSeqStmt(from);
 			break;

src/backend/nodes/equalfuncs.c

@@ -1546,6 +1546,15 @@ _equalReplicaIdentityStmt(const ReplicaIdentityStmt *a, const ReplicaIdentityStm
 	return true;
 }
 
+static bool
+_equalAlterSystemStmt(const AlterSystemStmt * a, const AlterSystemStmt * b)
+{
+	COMPARE_NODE_FIELD(setstmt);
+
+	return true;
+}
+
+
 static bool
 _equalCreateSeqStmt(const CreateSeqStmt *a, const CreateSeqStmt *b)
 {
@@ -2838,6 +2847,9 @@ equal(const void *a, const void *b)
 		case T_ReplicaIdentityStmt:
 			retval = _equalReplicaIdentityStmt(a, b);
 			break;
+		case T_AlterSystemStmt:
+			retval = _equalAlterSystemStmt(a, b);
+			break;
 		case T_CreateSeqStmt:
 			retval = _equalCreateSeqStmt(a, b);
 			break;

src/backend/parser/gram.y

@@ -216,7 +216,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 		AlterEventTrigStmt
 		AlterDatabaseStmt AlterDatabaseSetStmt AlterDomainStmt AlterEnumStmt
 		AlterFdwStmt AlterForeignServerStmt AlterGroupStmt
-		AlterObjectSchemaStmt AlterOwnerStmt AlterSeqStmt AlterTableStmt
+		AlterObjectSchemaStmt AlterOwnerStmt AlterSeqStmt AlterSystemStmt AlterTableStmt
 		AlterExtensionStmt AlterExtensionContentsStmt AlterForeignTableStmt
 		AlterCompositeTypeStmt AlterUserStmt AlterUserMappingStmt AlterUserSetStmt
 		AlterRoleStmt AlterRoleSetStmt
@@ -397,7 +397,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 %type <istmt>	insert_rest
 
-%type <vsetstmt> set_rest set_rest_more SetResetClause FunctionSetResetClause
+%type <vsetstmt> generic_set set_rest set_rest_more SetResetClause FunctionSetResetClause
 
 %type <node>	TableElement TypedTableElement ConstraintElem TableFuncElement
 %type <node>	columnDef columnOptions
@@ -724,6 +724,7 @@ stmt :
 			| AlterObjectSchemaStmt
 			| AlterOwnerStmt
 			| AlterSeqStmt
+			| AlterSystemStmt
 			| AlterTableStmt
 			| AlterCompositeTypeStmt
 			| AlterRoleSetStmt
@@ -1333,7 +1334,7 @@ set_rest:
 			| set_rest_more
 			;
 
-set_rest_more:	/* Generic SET syntaxes: */
+generic_set:
 			var_name TO var_list
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
@@ -1364,6 +1365,9 @@ set_rest_more:	/* Generic SET syntaxes: */
 					n->name = $1;
 					$$ = n;
 				}
+
+set_rest_more:	/* Generic SET syntaxes: */
+			generic_set 						{$$ = $1;}
 			| var_name FROM CURRENT_P
 				{
 					VariableSetStmt *n = makeNode(VariableSetStmt);
@@ -8310,6 +8314,23 @@ DropdbStmt: DROP DATABASE database_name
 		;
 
 
+/*****************************************************************************
+ *
+ *		ALTER SYSTEM SET
+ *
+ * This is used to change configuration parameters persistently.
+ *****************************************************************************/
+
+AlterSystemStmt:
+			ALTER SYSTEM_P SET generic_set
+				{
+					AlterSystemStmt *n = makeNode(AlterSystemStmt);
+					n->setstmt = $4;
+					$$ = (Node *)n;
+				}
+		;
+
+
 /*****************************************************************************
  *
  * Manipulate a domain

src/backend/replication/basebackup.c

@@ -811,6 +811,13 @@ sendDir(char *path, int basepathlen, bool sizeonly)
 					strlen(PG_TEMP_FILE_PREFIX)) == 0)
 			continue;
 
+		/* skip auto conf temporary file */
+		if (strncmp(de->d_name,
+					PG_AUTOCONF_FILENAME ".temp",
+					sizeof(PG_AUTOCONF_FILENAME) + 4) == 0)
+			continue;
+
+
 		/*
 		 * If there's a backup_label file, it belongs to a backup started by
 		 * the user with pg_start_backup(). It is *not* correct for this

src/backend/tcop/utility.c

@@ -687,6 +687,11 @@ standard_ProcessUtility(Node *parsetree,
 			ExplainQuery((ExplainStmt *) parsetree, queryString, params, dest);
 			break;
 
+		case T_AlterSystemStmt:
+			PreventTransactionChain(isTopLevel, "ALTER SYSTEM");
+			AlterSystemSetConfigFile((AlterSystemStmt *) parsetree);
+			break;
+
 		case T_VariableSetStmt:
 			ExecSetVariableStmt((VariableSetStmt *) parsetree, isTopLevel);
 			break;
@@ -2157,6 +2162,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "REFRESH MATERIALIZED VIEW";
 			break;
 
+		case T_AlterSystemStmt:
+			tag = "ALTER SYSTEM";
+			break;
+
 		case T_VariableSetStmt:
 			switch (((VariableSetStmt *) parsetree)->kind)
 			{
@@ -2726,6 +2735,10 @@ GetCommandLogLevel(Node *parsetree)
 			lev = LOGSTMT_DDL;
 			break;
 
+		case T_AlterSystemStmt:
+			lev = LOGSTMT_ALL;
+			break;
+
 		case T_VariableSetStmt:
 			lev = LOGSTMT_ALL;
 			break;

src/backend/utils/misc/guc-file.l

@@ -120,6 +120,9 @@ ProcessConfigFile(GucContext context)
 				   *head,
 				   *tail;
 	int			i;
+	char		ConfigAutoFileName[MAXPGPATH];
+	char		*ErrorConfFile;
+	char		*CallingFileName;
 
 	/*
 	 * Config files are processed on startup (by the postmaster only)
@@ -134,6 +137,8 @@ ProcessConfigFile(GucContext context)
 	 */
 	elevel = IsUnderPostmaster ? DEBUG2 : LOG;
 
+	ErrorConfFile = ConfigFileName;
+
 	/* Parse the file into a list of option names and values */
 	head = tail = NULL;
 
@@ -144,6 +149,26 @@ ProcessConfigFile(GucContext context)
 		goto cleanup_list;
 	}
 
+	/*
+	 * Parse postgresql.auto.conf file after postgresql.conf to replace
+	 * parameters set by ALTER SYSTEM command. This file is present in
+	 * data directory, however when called during initdb data directory is not
+	 * set till this point, so use ConfigFile path which will be same.
+	 */
+	snprintf(ConfigAutoFileName,sizeof(ConfigAutoFileName),"%s", PG_AUTOCONF_FILENAME);
+	if (data_directory)
+		CallingFileName = NULL;
+	else
+		CallingFileName = ConfigFileName;
+
+	if (!ParseConfigFile(ConfigAutoFileName, CallingFileName, false, 0, elevel, &head, &tail))
+	{
+		/* Syntax error(s) detected in the file, so bail out */
+		error = true;
+		ErrorConfFile = ConfigAutoFileName;
+		goto cleanup_list;
+	}
+
 	/*
 	 * Mark all extant GUC variables as not present in the config file.
 	 * We need this so that we can tell below which ones have been removed
@@ -192,6 +217,7 @@ ProcessConfigFile(GucContext context)
 							item->name,
 							item->filename, item->sourceline)));
 			error = true;
+			ErrorConfFile = item->filename;
 		}
 	}
 
@@ -318,7 +344,10 @@ ProcessConfigFile(GucContext context)
 			}
 		}
 		else if (scres == 0)
+		{
 			error = true;
+			ErrorConfFile = item->filename;
+		}
 		/* else no error but variable's active value was not changed */
 
 		/*
@@ -348,17 +377,17 @@ ProcessConfigFile(GucContext context)
 			ereport(ERROR,
 					(errcode(ERRCODE_CONFIG_FILE_ERROR),
 					 errmsg("configuration file \"%s\" contains errors",
-							ConfigFileName)));
+							ErrorConfFile)));
 		else if (apply)
 			ereport(elevel,
 					(errcode(ERRCODE_CONFIG_FILE_ERROR),
 					 errmsg("configuration file \"%s\" contains errors; unaffected changes were applied",
-							ConfigFileName)));
+							ErrorConfFile)));
 		else
 			ereport(elevel,
 					(errcode(ERRCODE_CONFIG_FILE_ERROR),
 					 errmsg("configuration file \"%s\" contains errors; no changes were applied",
-							ConfigFileName)));
+							ErrorConfFile)));
 	}
 }
 

src/bin/initdb/initdb.c

@@ -1228,6 +1228,7 @@ setup_config(void)
 	char		repltok[MAXPGPATH];
 	char		path[MAXPGPATH];
 	const char *default_timezone;
+	char	   *autoconflines[3];
 
 	fputs(_("creating configuration files ... "), stdout);
 	fflush(stdout);
@@ -1320,6 +1321,21 @@ setup_config(void)
 	writefile(path, conflines);
 	chmod(path, S_IRUSR | S_IWUSR);
 
+	/*
+	 * create the automatic configuration file to store the configuration
+	 * parameters set by ALTER SYSTEM command. The parameters present in this
+	 * file will override the value of parameters that exists before parse of
+	 * this file.
+	 */
+	autoconflines[0] = pg_strdup("# Do not edit this file manually! \n");
+	autoconflines[1] = pg_strdup("# It will be overwritten by the ALTER SYSTEM command. \n");
+	autoconflines[2] = NULL;
+
+	sprintf(path, "%s/%s", pg_data, PG_AUTOCONF_FILENAME);
+
+	writefile(path, autoconflines);
+	chmod(path, S_IRUSR | S_IWUSR);
+
 	free(conflines);
 
 

src/include/nodes/nodes.h

@@ -363,6 +363,7 @@ typedef enum NodeTag
 	T_AlterEventTrigStmt,
 	T_RefreshMatViewStmt,
 	T_ReplicaIdentityStmt,
+	T_AlterSystemStmt,
 
 	/*
 	 * TAGS FOR PARSE TREE NODES (parsenodes.h)

src/include/nodes/parsenodes.h

@@ -2471,6 +2471,16 @@ typedef struct DropdbStmt
 	bool		missing_ok;		/* skip error if db is missing? */
 } DropdbStmt;
 
+/* ----------------------
+ *		Alter System Statement
+ * ----------------------
+ */
+typedef struct AlterSystemStmt
+{
+	NodeTag		type;
+	VariableSetStmt *setstmt;	/* SET subcommand */
+}	AlterSystemStmt;
+
 /* ----------------------
  *		Cluster Statement (support pbrown's cluster index implementation)
  * ----------------------

src/include/pg_config_manual.h

@@ -292,3 +292,10 @@
 /* #define HEAPDEBUGALL */
 /* #define ACLDEBUG */
 /* #define RTDEBUG */
+
+/*
+ * Automatic configuration file name for ALTER SYSTEM.
+ * This file will be used to store values of configuration parameters
+ * set by ALTER SYSTEM command
+ */
+#define PG_AUTOCONF_FILENAME		"postgresql.auto.conf"

src/include/storage/lwlock.h

@@ -81,6 +81,7 @@ typedef enum LWLockId
 	SyncRepLock,
 	BackgroundWorkerLock,
 	DynamicSharedMemoryControlLock,
+	AutoFileLock,
 	/* Individual lock IDs end here */
 	FirstBufMappingLock,
 	FirstLockMgrLock = FirstBufMappingLock + NUM_BUFFER_PARTITIONS,

src/include/utils/guc.h

@@ -326,6 +326,7 @@ extern bool parse_real(const char *value, double *result);
 extern int set_config_option(const char *name, const char *value,
 				  GucContext context, GucSource source,
 				  GucAction action, bool changeVal, int elevel);
+extern void AlterSystemSetConfigFile(AlterSystemStmt * setstmt);
 extern char *GetConfigOptionByName(const char *name, const char **varname);
 extern void GetConfigOptionByNum(int varnum, const char **values, bool *noshow);
 extern int	GetNumConfigOptions(void);