Rename the newly-added commands for discarding session state.

RESET SESSION, RESET PLANS, and RESET TEMP are now DISCARD ALL,
DISCARD PLANS, and DISCARD TEMP, respectively. This is to avoid
confusion with the pre-existing RESET variants: the DISCARD
commands are not actually similar to RESET. Patch from Marko
Kreen, with some minor editorialization.

19 files changed, 331 insertions, 119 deletions

diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml
index fd1360219e..8bfa76aed8 100644
--- a/doc/src/sgml/ref/allfiles.sgml
+++ b/doc/src/sgml/ref/allfiles.sgml
@@ -61,6 +61,7 @@ Complete list of usable sgml source files in this directory.
 <!entity deallocate         system "deallocate.sgml">
 <!entity declare            system "declare.sgml">
 <!entity delete             system "delete.sgml">
+<!entity discard            system "discard.sgml">
 <!entity dropAggregate      system "drop_aggregate.sgml">
 <!entity dropCast           system "drop_cast.sgml">
 <!entity dropConversion     system "drop_conversion.sgml">
diff --git a/doc/src/sgml/ref/discard.sgml b/doc/src/sgml/ref/discard.sgml
new file mode 100644
index 0000000000..d1e149261b
--- /dev/null
+++ b/doc/src/sgml/ref/discard.sgml
@@ -0,0 +1,107 @@
+<!--
+$PostgreSQL$
+PostgreSQL documentation
+-->
+
+<refentry id="SQL-DISCARD">
+ <refmeta>
+  <refentrytitle id="SQL-DISCARD-TITLE">DISCARD</refentrytitle>
+  <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>DISCARD</refname>
+  <refpurpose>Discard internal server state</refpurpose>
+ </refnamediv>
+
+ <indexterm zone="sql-discard">
+  <primary>DISCARD</primary>
+ </indexterm>
+
+ <refsynopsisdiv>
+<synopsis>
+DISCARD { ALL | PLANS | TEMPORARY | TEMP }
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <para>
+   <command>DISCARD</> releases internal resources associated with a
+   database session. These resources are normally released at the end
+   of the session.
+  </para>
+
+  <para>
+   <command>DISCARD TEMP</> drops all temporary tables created in the
+   current session.  <command>DISCARD PLANS</> releases all internally
+   cached query plans.  <command>DISCARD ALL</> resets a session to
+   its original state, discarding temporary resources and resetting
+   session-local configuration changes.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Parameters</title>
+
+  <variablelist>
+
+   <varlistentry>
+    <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></term>
+    <listitem>
+     <para>
+      Drops all temporary tables created in the current session.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>PLANS</literal></term>
+    <listitem>
+     <para>
+      Releases all cached query plans.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>ALL</literal></term>
+    <listitem>
+     <para>
+      Releases all temporary resources associated with the current
+      session and resets the session to its initial state. This has
+      the same effect as executing the following sequence of
+      statements:
+<programlisting>
+SET SESSION AUTHORIZATION DEFAULT;
+RESET ALL;
+DEALLOCATE ALL;
+CLOSE ALL;
+UNLISTEN *;
+DISCARD PLANS;
+DISCARD TEMP;
+</programlisting>
+     </para>
+    </listitem>
+   </varlistentry>
+
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Notes</title>
+
+   <para>
+    <command>DISCARD ALL</> cannot be executed inside a transaction block.
+   </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Compatibility</title>
+
+  <para>
+   <command>DISCARD</command> is a <productname>PostgreSQL</productname> extension.
+  </para>
+ </refsect1>
+</refentry>
diff --git a/doc/src/sgml/ref/reset.sgml b/doc/src/sgml/ref/reset.sgml
index 544676671e..df97f43d34 100644
--- a/doc/src/sgml/ref/reset.sgml
+++ b/doc/src/sgml/ref/reset.sgml
@@ -22,7 +22,6 @@ PostgreSQL documentation
 <synopsis>
 RESET <replaceable class="PARAMETER">configuration_parameter</replaceable>
 RESET ALL
-RESET { PLANS | SESSION | TEMP | TEMPORARY }
 </synopsis>
  </refsynopsisdiv>
 
@@ -53,15 +52,6 @@ SET <replaceable class="parameter">configuration_parameter</replaceable> TO DEFA
    See the <command>SET</> reference page for details on the
    transaction behavior of <command>RESET</>.
   </para>
-
-  <para>
-   <command>RESET</> can also be used to release internal resources
-   that are usually released at the end of session.  <command>RESET
-   TEMP</> drops all temporary tables created in the current session.
-   <command>RESET PLANS</> releases all internally cached plans.
-   <command>RESET SESSION</> releases all externally visible temporary
-   resources associated with the current session.
-  </para>
  </refsect1>
 
  <refsect1>
@@ -86,57 +76,10 @@ SET <replaceable class="parameter">configuration_parameter</replaceable> TO DEFA
      </para>
     </listitem>
    </varlistentry>
-
-   <varlistentry>
-    <term><literal>TEMP, TEMPORARY</literal></term>
-    <listitem>
-     <para>
-      Drops all temporary tables created in the current session.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>PLANS</literal></term>
-    <listitem>
-     <para>
-      Releases all cached query plans.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>SESSION</literal></term>
-    <listitem>
-     <para>
-      Releases all temporary resources associated with the current
-      session. This has the same effect as executing the following
-      command sequence:
-<programlisting>
-SET SESSION AUTHORIZATION DEFAULT;
-RESET ALL;
-DEALLOCATE ALL;
-CLOSE ALL;
-UNLISTEN *;
-RESET PLANS;
-RESET TEMP;
-</programlisting>
-     </para>
-    </listitem>
-   </varlistentry>
-
   </variablelist>
  </refsect1>
 
  <refsect1>
-  <title>Notes</title>
-
-   <para>
-    <command>RESET SESSION</> cannot be executed inside a transaction block.
-   </para>
- </refsect1>
-
- <refsect1>
   <title>Examples</title>
 
   <para>
diff --git a/doc/src/sgml/reference.sgml b/doc/src/sgml/reference.sgml
index 87ba1e0027..dc3f117161 100644
--- a/doc/src/sgml/reference.sgml
+++ b/doc/src/sgml/reference.sgml
@@ -89,6 +89,7 @@
    &deallocate;
    &declare;
    &delete;
+   &discard;
    &dropAggregate;
    &dropCast;
    &dropConversion;
diff --git a/src/backend/commands/Makefile b/src/backend/commands/Makefile
index 4bf0b965c3..4e46d7db96 100644
--- a/src/backend/commands/Makefile
+++ b/src/backend/commands/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 OBJS = aggregatecmds.o alter.o analyze.o async.o cluster.o comment.o  \
 	conversioncmds.o copy.o \
-	dbcommands.o define.o explain.o functioncmds.o \
+	dbcommands.o define.o discard.o explain.o functioncmds.o \
 	indexcmds.o lockcmds.o operatorcmds.o opclasscmds.o \
 	portalcmds.o prepare.o proclang.o \
 	schemacmds.o sequence.o tablecmds.o tablespace.o trigger.o \
diff --git a/src/backend/commands/discard.c b/src/backend/commands/discard.c
new file mode 100644
index 0000000000..3f05361f3d
--- /dev/null
+++ b/src/backend/commands/discard.c
@@ -0,0 +1,71 @@
+/*-------------------------------------------------------------------------
+ *
+ * discard.c
+ *	  The implementation of the DISCARD command
+ *
+ * Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL$
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/xact.h"
+#include "catalog/namespace.h"
+#include "commands/async.h"
+#include "commands/discard.h"
+#include "commands/prepare.h"
+#include "commands/variable.h"
+#include "utils/plancache.h"
+#include "utils/portal.h"
+
+static void DiscardAll(bool isTopLevel);
+
+/*
+ * DISCARD { ALL | TEMP | PLANS }
+ */
+void
+DiscardCommand(DiscardStmt *stmt, bool isTopLevel)
+{
+	switch (stmt->target)
+	{
+		case DISCARD_ALL:
+			DiscardAll(isTopLevel);
+			break;
+
+		case DISCARD_PLANS:
+			ResetPlanCache();
+			break;
+
+		case DISCARD_TEMP:
+			ResetTempTableNamespace();
+			break;
+
+		default:
+			elog(ERROR, "unrecognized DISCARD target: %d", stmt->target);
+	}
+}
+
+static void
+DiscardAll(bool isTopLevel)
+{
+	/*
+	 * Disallow DISCARD ALL in a transaction block. This is arguably
+	 * inconsistent (we don't make a similar check in the command
+	 * sequence that DISCARD ALL is equivalent to), but the idea is
+	 * to catch mistakes: DISCARD ALL inside a transaction block
+	 * would leave the transaction still uncommitted.
+	 */
+	PreventTransactionChain(isTopLevel, "DISCARD ALL");
+
+	SetPGVariable("session_authorization", NIL, false);
+	ResetAllOptions();
+	DropAllPreparedStatements();
+	PortalHashTableDeleteAll();
+	Async_UnlistenAll();
+	ResetPlanCache();
+	ResetTempTableNamespace();
+}
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 1648713307..c516aebd6a 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -2589,6 +2589,16 @@ _copyVariableResetStmt(VariableResetStmt *from)
 	return newnode;
 }
 
+static DiscardStmt *
+_copyDiscardStmt(DiscardStmt *from)
+{
+	DiscardStmt *newnode = makeNode(DiscardStmt);
+
+	COPY_SCALAR_FIELD(target);
+
+	return newnode;
+}
+
 static CreateTableSpaceStmt *
 _copyCreateTableSpaceStmt(CreateTableSpaceStmt *from)
 {
@@ -3380,6 +3390,9 @@ copyObject(void *from)
 		case T_VariableResetStmt:
 			retval = _copyVariableResetStmt(from);
 			break;
+		case T_DiscardStmt:
+			retval = _copyDiscardStmt(from);
+			break;
 		case T_CreateTableSpaceStmt:
 			retval = _copyCreateTableSpaceStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 0af004ad1d..c927159fdd 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1377,6 +1377,14 @@ _equalVariableResetStmt(VariableResetStmt *a, VariableResetStmt *b)
 }
 
 static bool
+_equalDiscardStmt(DiscardStmt *a, DiscardStmt *b)
+{
+	COMPARE_SCALAR_FIELD(target);
+
+	return true;
+}
+
+static bool
 _equalCreateTableSpaceStmt(CreateTableSpaceStmt *a, CreateTableSpaceStmt *b)
 {
 	COMPARE_STRING_FIELD(tablespacename);
@@ -2313,6 +2321,9 @@ equal(void *a, void *b)
 		case T_VariableResetStmt:
 			retval = _equalVariableResetStmt(a, b);
 			break;
+		case T_DiscardStmt:
+			retval = _equalDiscardStmt(a, b);
+			break;
 		case T_CreateTableSpaceStmt:
 			retval = _equalCreateTableSpaceStmt(a, b);
 			break;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index bc8006d7ec..686be4d88d 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -158,7 +158,7 @@ static Node *makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args)
 		CreateOpFamilyStmt AlterOpFamilyStmt CreatePLangStmt
 		CreateSchemaStmt CreateSeqStmt CreateStmt CreateTableSpaceStmt
 		CreateAssertStmt CreateTrigStmt CreateUserStmt CreateRoleStmt
-		CreatedbStmt DeclareCursorStmt DefineStmt DeleteStmt
+		CreatedbStmt DeclareCursorStmt DefineStmt DeleteStmt DiscardStmt
 		DropGroupStmt DropOpClassStmt DropOpFamilyStmt DropPLangStmt DropStmt
 		DropAssertStmt DropTrigStmt DropRuleStmt DropCastStmt DropRoleStmt
 		DropUserStmt DropdbStmt DropTableSpaceStmt ExplainStmt FetchStmt
@@ -382,7 +382,7 @@ static Node *makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args)
 
 	DATABASE DAY_P DEALLOCATE DEC DECIMAL_P DECLARE DEFAULT DEFAULTS
 	DEFERRABLE DEFERRED DEFINER DELETE_P DELIMITER DELIMITERS
-	DESC DISABLE_P DISTINCT DO DOCUMENT_P DOMAIN_P DOUBLE_P DROP
+	DESC DISABLE_P DISCARD DISTINCT DO DOCUMENT_P DOMAIN_P DOUBLE_P DROP
 
 	EACH ELSE ENABLE_P ENCODING ENCRYPTED END_P ENUM_P ESCAPE EXCEPT EXCLUDING
 	EXCLUSIVE EXECUTE EXISTS EXPLAIN EXTERNAL EXTRACT
@@ -416,7 +416,7 @@ static Node *makeXmlExpr(XmlExprOp op, char *name, List *named_args, List *args)
 	OBJECT_P OF OFF OFFSET OIDS OLD ON ONLY OPERATOR OPTION OR
 	ORDER OUT_P OUTER_P OVERLAPS OVERLAY OWNED OWNER
 
-	PARTIAL PASSWORD PLACING POSITION
+	PARTIAL PASSWORD PLACING PLANS POSITION
 	PRECISION PRESERVE PREPARE PREPARED PRIMARY
 	PRIOR PRIVILEGES PROCEDURAL PROCEDURE
 
@@ -569,6 +569,7 @@ stmt :
 			| DeclareCursorStmt
 			| DefineStmt
 			| DeleteStmt
+			| DiscardStmt
 			| DropAssertStmt
 			| DropCastStmt
 			| DropGroupStmt
@@ -1330,6 +1331,40 @@ CheckPointStmt:
 
 /*****************************************************************************
  *
+ * DISCARD { ALL | TEMP | PLANS }
+ *
+ *****************************************************************************/
+
+DiscardStmt:
+			DISCARD ALL
+				{
+					DiscardStmt *n = makeNode(DiscardStmt);
+					n->target = DISCARD_ALL;
+					$$ = (Node *) n;
+				}
+			| DISCARD TEMP
+				{
+					DiscardStmt *n = makeNode(DiscardStmt);
+					n->target = DISCARD_TEMP;
+					$$ = (Node *) n;
+				}
+			| DISCARD TEMPORARY
+				{
+					DiscardStmt *n = makeNode(DiscardStmt);
+					n->target = DISCARD_TEMP;
+					$$ = (Node *) n;
+				}
+			| DISCARD PLANS
+				{
+					DiscardStmt *n = makeNode(DiscardStmt);
+					n->target = DISCARD_PLANS;
+					$$ = (Node *) n;
+				}
+		;
+
+
+/*****************************************************************************
+ *
  *	ALTER [ TABLE | INDEX ] variations
  *
  *****************************************************************************/
@@ -8796,6 +8831,7 @@ unreserved_keyword:
 			| DELIMITER
 			| DELIMITERS
 			| DISABLE_P
+			| DISCARD
 			| DOCUMENT_P
 			| DOMAIN_P
 			| DOUBLE_P
@@ -8881,6 +8917,7 @@ unreserved_keyword:
 			| OWNER
 			| PARTIAL
 			| PASSWORD
+			| PLANS
 			| PREPARE
 			| PREPARED
 			| PRESERVE
diff --git a/src/backend/parser/keywords.c b/src/backend/parser/keywords.c
index 6a1ca7f3a8..a4ecd7303d 100644
--- a/src/backend/parser/keywords.c
+++ b/src/backend/parser/keywords.c
@@ -124,6 +124,7 @@ static const ScanKeyword ScanKeywords[] = {
 	{"delimiters", DELIMITERS},
 	{"desc", DESC},
 	{"disable", DISABLE_P},
+	{"discard", DISCARD},
 	{"distinct", DISTINCT},
 	{"do", DO},
 	{"document", DOCUMENT_P},
@@ -269,6 +270,7 @@ static const ScanKeyword ScanKeywords[] = {
 	{"partial", PARTIAL},
 	{"password", PASSWORD},
 	{"placing", PLACING},
+	{"plans", PLANS},
 	{"position", POSITION},
 	{"precision", PRECISION},
 	{"prepare", PREPARE},
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 26bf62fa93..2221083118 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -29,6 +29,7 @@
 #include "commands/copy.h"
 #include "commands/dbcommands.h"
 #include "commands/defrem.h"
+#include "commands/discard.h"
 #include "commands/explain.h"
 #include "commands/lockcmds.h"
 #include "commands/portalcmds.h"
@@ -604,10 +605,7 @@ ProcessUtility(Node *parsetree,
 							break;
 
 						case OBJECT_DOMAIN:
-
-							/*
-							 * RemoveDomain does its own permissions checks
-							 */
+							/* RemoveDomain does its own permissions checks */
 							RemoveDomain(names, stmt->behavior,
 										 stmt->missing_ok);
 							break;
@@ -618,10 +616,7 @@ ProcessUtility(Node *parsetree,
 							break;
 
 						case OBJECT_SCHEMA:
-
-							/*
-							 * RemoveSchema does its own permissions checks
-							 */
+							/* RemoveSchema does its own permissions checks */
 							RemoveSchema(names, stmt->behavior,
 										 stmt->missing_ok);
 							break;
@@ -994,6 +989,10 @@ ProcessUtility(Node *parsetree,
 			}
 			break;
 
+		case T_DiscardStmt:
+			DiscardCommand((DiscardStmt *) parsetree, isTopLevel);
+			break;
+
 		case T_CreateTrigStmt:
 			CreateTrigger((CreateTrigStmt *) parsetree, InvalidOid);
 			break;
@@ -1752,12 +1751,22 @@ CreateCommandTag(Node *parsetree)
 			break;
 
 		case T_VariableResetStmt:
-			{
-				VariableResetStmt *stmt = (VariableResetStmt *) parsetree;
-				if (pg_strcasecmp(stmt->name, "session") == 0)
-					tag = "RESET SESSION";
-				else
-					tag = "RESET";
+			tag = "RESET";
+			break;
+
+		case T_DiscardStmt:
+			switch (((DiscardStmt *) parsetree)->target) {
+				case DISCARD_ALL:
+					tag = "DISCARD ALL";
+					break;
+				case DISCARD_PLANS:
+					tag = "DISCARD PLANS";
+					break;
+				case DISCARD_TEMP:
+					tag = "DISCARD TEMP";
+					break;
+				default:
+					tag = "???";
 			}
 			break;
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index fd0abf9e9f..31fbb949fc 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -5048,30 +5048,6 @@ GetPGVariableResultDesc(const char *name)
 }
 
 /*
- * RESET SESSION command.
- */
-static void
-ResetSession(bool isTopLevel)
-{
-	/*
-	 * Disallow RESET SESSION in a transaction block. This is arguably
-	 * inconsistent (we don't make a similar check in the command
-	 * sequence that RESET SESSION is equivalent to), but the idea is
-	 * to catch mistakes: RESET SESSION inside a transaction block
-	 * would leave the transaction still uncommitted.
-	 */
-	PreventTransactionChain(isTopLevel, "RESET SESSION");
-
-	SetPGVariable("session_authorization", NIL, false);
-	ResetAllOptions();
-	DropAllPreparedStatements();
-	PortalHashTableDeleteAll();
-	Async_UnlistenAll();
-	ResetPlanCache();
-	ResetTempTableNamespace();
-}
-
-/*
  * RESET command
  */
 void
@@ -5079,13 +5055,6 @@ ResetPGVariable(const char *name, bool isTopLevel)
 {
 	if (pg_strcasecmp(name, "all") == 0)
 		ResetAllOptions();
-	else if (pg_strcasecmp(name, "session") == 0)
-		ResetSession(isTopLevel);
-	else if (pg_strcasecmp(name, "temp") == 0 ||
-			 pg_strcasecmp(name, "temporary") == 0)
-		ResetTempTableNamespace();
-	else if (pg_strcasecmp(name, "plans") == 0)
-		ResetPlanCache();
 	else
 		set_config_option(name,
 						  NULL,
diff --git a/src/backend/utils/mmgr/portalmem.c b/src/backend/utils/mmgr/portalmem.c
index d4952e51ee..40af72e11d 100644
--- a/src/backend/utils/mmgr/portalmem.c
+++ b/src/backend/utils/mmgr/portalmem.c
@@ -455,7 +455,7 @@ PortalDrop(Portal portal, bool isTopCommit)
 /*
  * Delete all declared cursors.
  *
- * Used by commands: CLOSE ALL, RESET SESSION
+ * Used by commands: CLOSE ALL, DISCARD ALL
  */
 void
 PortalHashTableDeleteAll(void)
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 63c4b06849..c3e7daf406 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -527,8 +527,8 @@ psql_completion(char *text, int start, int end)
 	static const char *const sql_commands[] = {
 		"ABORT", "ALTER", "ANALYZE", "BEGIN", "CHECKPOINT", "CLOSE", "CLUSTER",
 		"COMMENT", "COMMIT", "COPY", "CREATE", "DEALLOCATE", "DECLARE",
-		"DELETE FROM", "DROP", "END", "EXECUTE", "EXPLAIN", "FETCH", "GRANT",
-		"INSERT", "LISTEN", "LOAD", "LOCK", "MOVE", "NOTIFY", "PREPARE",
+		"DELETE FROM", "DISCARD", "DROP", "END", "EXECUTE", "EXPLAIN", "FETCH",
+		"GRANT", "INSERT", "LISTEN", "LOAD", "LOCK", "MOVE", "NOTIFY", "PREPARE",
 		"REASSIGN", "REINDEX", "RELEASE", "RESET", "REVOKE", "ROLLBACK",
 		"SAVEPOINT", "SELECT", "SET", "SHOW", "START", "TRUNCATE", "UNLISTEN",
 		"UPDATE", "VACUUM", NULL
@@ -1244,6 +1244,15 @@ psql_completion(char *text, int start, int end)
 	}
 	/* XXX: implement tab completion for DELETE ... USING */
 
+/* DISCARD */
+	else if (pg_strcasecmp(prev_wd, "DISCARD") == 0)
+	{
+		static const char *const list_DISCARD[] =
+		{"ALL", "PLANS", "TEMP", NULL};
+
+		COMPLETE_WITH_LIST(list_DISCARD);
+	}
+
 /* DROP (when not the previous word) */
 	/* DROP AGGREGATE */
 	else if (pg_strcasecmp(prev3_wd, "DROP") == 0 &&
diff --git a/src/include/commands/discard.h b/src/include/commands/discard.h
new file mode 100644
index 0000000000..6fa5c57fb2
--- /dev/null
+++ b/src/include/commands/discard.h
@@ -0,0 +1,20 @@
+/*-------------------------------------------------------------------------
+ *
+ * discard.h
+ *	  prototypes for discard.c.
+ *
+ *
+ * Copyright (c) 1996-2007, PostgreSQL Global Development Group
+ *
+ * $PostgreSQL$
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DISCARD_H
+#define DISCARD_H
+
+#include "nodes/parsenodes.h"
+
+extern void DiscardCommand(DiscardStmt *stmt, bool isTopLevel);
+
+#endif   /* DISCARD_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 0acf89443d..ab582dbbf9 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -273,6 +273,7 @@ typedef enum NodeTag
 	T_VariableSetStmt,
 	T_VariableShowStmt,
 	T_VariableResetStmt,
+	T_DiscardStmt,
 	T_CreateTrigStmt,
 	T_DropPropertyStmt,
 	T_CreatePLangStmt,
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b287376b98..e6c911929d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1871,6 +1871,24 @@ typedef struct VariableResetStmt
 } VariableResetStmt;
 
 /* ----------------------
+ * Discard Statement
+ * ----------------------
+ */
+
+typedef enum DiscardMode
+{
+	DISCARD_ALL,
+	DISCARD_PLANS,
+	DISCARD_TEMP
+} DiscardMode;
+
+typedef struct DiscardStmt
+{
+	NodeTag		type;
+	DiscardMode	target;
+} DiscardStmt;
+
+/* ----------------------
  *		LOCK Statement
  * ----------------------
  */
diff --git a/src/test/regress/expected/guc.out b/src/test/regress/expected/guc.out
index 484cc356e7..d8ad5667ab 100644
--- a/src/test/regress/expected/guc.out
+++ b/src/test/regress/expected/guc.out
@@ -426,7 +426,7 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
 (1 row)
 
 --
--- Test RESET TEMP
+-- Test DISCARD TEMP
 --
 CREATE TEMP TABLE reset_test ( data text ) ON COMMIT DELETE ROWS;
 SELECT relname FROM pg_class WHERE relname = 'reset_test';
@@ -435,14 +435,14 @@ SELECT relname FROM pg_class WHERE relname = 'reset_test';
  reset_test
 (1 row)
 
-RESET TEMP;
+DISCARD TEMP;
 SELECT relname FROM pg_class WHERE relname = 'reset_test';
  relname 
 ---------
 (0 rows)
 
 --
--- Test RESET SESSION
+-- Test DISCARD ALL
 --
 -- do changes
 DECLARE foo CURSOR WITH HOLD FOR SELECT 1;
@@ -489,8 +489,8 @@ SELECT current_user = 'temp_reset_user';
  t
 (1 row)
 
--- big RESET
-RESET SESSION;
+-- discard everything
+DISCARD ALL;
 -- look again
 SELECT relname FROM pg_listener;
  relname 
diff --git a/src/test/regress/sql/guc.sql b/src/test/regress/sql/guc.sql
index 274007a2c3..a25a13820d 100644
--- a/src/test/regress/sql/guc.sql
+++ b/src/test/regress/sql/guc.sql
@@ -125,15 +125,15 @@ SHOW datestyle;
 SELECT '2006-08-13 12:34:56'::timestamptz;
 
 --
--- Test RESET TEMP
+-- Test DISCARD TEMP
 --
 CREATE TEMP TABLE reset_test ( data text ) ON COMMIT DELETE ROWS;
 SELECT relname FROM pg_class WHERE relname = 'reset_test';
-RESET TEMP;
+DISCARD TEMP;
 SELECT relname FROM pg_class WHERE relname = 'reset_test';
 
 --
--- Test RESET SESSION
+-- Test DISCARD ALL
 --
 
 -- do changes
@@ -151,8 +151,8 @@ SELECT name FROM pg_cursors;
 SHOW vacuum_cost_delay;
 SELECT relname from pg_class where relname = 'tmp_foo';
 SELECT current_user = 'temp_reset_user';
--- big RESET
-RESET SESSION;
+-- discard everything
+DISCARD ALL;
 -- look again
 SELECT relname FROM pg_listener;
 SELECT name FROM pg_prepared_statements;