From 29a43f398afdbc8372452010b330f242d9ff298d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 22 Aug 2003 20:34:33 +0000
Subject: [PATCH] Tweak grammar to use FastAppend rather than lappend when
 constructing expr_lists.  This appears to be the only remaining O(N^2)
 bottleneck in processing many-way 'x IN (a,b,c,...)' conditions.

---
 src/backend/parser/gram.y   | 17 ++++++++++++++---
 src/include/nodes/pg_list.h |  8 +++++++-
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index ef6f8a80c5c..5bdbe012a95 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.429 2003/08/17 19:58:05 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.430 2003/08/22 20:34:33 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -108,6 +108,7 @@ static void doNegateFloat(Value *v);
 	DropBehavior		dbehavior;
 	OnCommitAction		oncommit;
 	List				*list;
+	FastList			fastlist;
 	Node				*node;
 	Value				*value;
 	ColumnRef			*columnref;
@@ -6719,8 +6720,18 @@ opt_indirection:
 				{ $$ = NIL; }
 		;
 
-expr_list:	a_expr									{ $$ = makeList1($1); }
-			| expr_list ',' a_expr					{ $$ = lappend($1, $3); }
+expr_list:	a_expr
+				{
+					FastList *dst = (FastList *) &$$;
+					makeFastList1(dst, $1);
+				}
+			| expr_list ',' a_expr
+				{
+					FastList *dst = (FastList *) &$$;
+					FastList *src = (FastList *) &$1;
+					*dst = *src;
+					FastAppend(dst, $3);
+				}
 		;
 
 extract_list:
diff --git a/src/include/nodes/pg_list.h b/src/include/nodes/pg_list.h
index 4d9ce8304b1..8ab22560ce6 100644
--- a/src/include/nodes/pg_list.h
+++ b/src/include/nodes/pg_list.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: pg_list.h,v 1.40 2003/08/08 21:42:48 momjian Exp $
+ * $Id: pg_list.h,v 1.41 2003/08/22 20:34:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -132,6 +132,9 @@ typedef struct List
  * FastList is an optimization for building large lists.  The conventional
  * way to build a list is repeated lappend() operations, but that is O(N^2)
  * in the number of list items, which gets tedious for large lists.
+ *
+ * Note: there are some hacks in gram.y that rely on the head pointer (the
+ * value-as-list) being the first field.
  */
 typedef struct FastList
 {
@@ -144,6 +147,9 @@ typedef struct FastList
 	( (fl)->head = (l), (fl)->tail = llastnode((fl)->head) )
 #define FastListValue(fl)	( (fl)->head )
 
+#define makeFastList1(fl, x1)  \
+	( (fl)->head = (fl)->tail = makeList1(x1) )
+
 
 /*
  * function prototypes in nodes/list.c