Reimplement the linked list data structure used throughout the backend.

In the past, we used a 'Lispy' linked list implementation: a "list" was
merely a pointer to the head node of the list. The problem with that
design is that it makes lappend() and length() linear time. This patch
fixes that problem (and others) by maintaining a count of the list
length and a pointer to the tail node along with each head node pointer.
A "list" is now a pointer to a structure containing some meta-data
about the list; the head and tail pointers in that structure refer
to ListCell structures that maintain the actual linked list of nodes.

The function names of the list API have also been changed to, I hope,
be more logically consistent. By default, the old function names are
still available; they will be disabled-by-default once the rest of
the tree has been updated to use the new API names.

1 files changed, 21 insertions, 22 deletions

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 619013a18d5..3bad7a4f601 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.104 2004/04/25 18:23:56 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.105 2004/05/26 04:41:27 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -200,7 +200,7 @@ void
 set_cheapest(RelOptInfo *parent_rel)
 {
 	List	   *pathlist = parent_rel->pathlist;
-	List	   *p;
+	ListCell   *p;
 	Path	   *cheapest_startup_path;
 	Path	   *cheapest_total_path;
 
@@ -209,9 +209,9 @@ set_cheapest(RelOptInfo *parent_rel)
 	if (pathlist == NIL)
 		elog(ERROR, "could not devise a query plan for the given query");
 
-	cheapest_startup_path = cheapest_total_path = (Path *) lfirst(pathlist);
+	cheapest_startup_path = cheapest_total_path = (Path *) linitial(pathlist);
 
-	foreach(p, lnext(pathlist))
+	for_each_cell(p, lnext(list_head(pathlist)))
 	{
 		Path	   *path = (Path *) lfirst(p);
 		int			cmp;
@@ -269,17 +269,17 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
 {
 	bool		accept_new = true;		/* unless we find a superior old
 										 * path */
-	List	   *insert_after = NIL;		/* where to insert new item */
-	List	   *p1_prev = NIL;
-	List	   *p1;
+	ListCell   *insert_after = NULL;	/* where to insert new item */
+	ListCell   *p1_prev = NULL;
+	ListCell   *p1;
 
 	/*
 	 * Loop to check proposed new path against old paths.  Note it is
 	 * possible for more than one old path to be tossed out because
 	 * new_path dominates it.
 	 */
-	p1 = parent_rel->pathlist;	/* cannot use foreach here */
-	while (p1 != NIL)
+	p1 = list_head(parent_rel->pathlist);	/* cannot use foreach here */
+	while (p1 != NULL)
 	{
 		Path	   *old_path = (Path *) lfirst(p1);
 		bool		remove_old = false; /* unless new proves superior */
@@ -346,15 +346,14 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
 		 */
 		if (remove_old)
 		{
-			List	   *p1_next = lnext(p1);
-
+			parent_rel->pathlist = list_delete_cell(parent_rel->pathlist,
+													p1, p1_prev);
+			/* Delete the data pointed-to by the deleted cell */
+			pfree(old_path);
 			if (p1_prev)
-				lnext(p1_prev) = p1_next;
+				p1 = lnext(p1_prev);
 			else
-				parent_rel->pathlist = p1_next;
-			pfree(old_path);
-			pfree(p1);			/* this is why we can't use foreach */
-			p1 = p1_next;
+				p1 = list_head(parent_rel->pathlist);
 		}
 		else
 		{
@@ -378,7 +377,7 @@ add_path(RelOptInfo *parent_rel, Path *new_path)
 	{
 		/* Accept the new path: insert it at proper place in pathlist */
 		if (insert_after)
-			lnext(insert_after) = lcons(new_path, lnext(insert_after));
+			lappend_cell(parent_rel->pathlist, insert_after, new_path);
 		else
 			parent_rel->pathlist = lcons(new_path, parent_rel->pathlist);
 	}
@@ -508,7 +507,7 @@ AppendPath *
 create_append_path(RelOptInfo *rel, List *subpaths)
 {
 	AppendPath *pathnode = makeNode(AppendPath);
-	List	   *l;
+	ListCell   *l;
 
 	pathnode->path.pathtype = T_Append;
 	pathnode->path.parent = rel;
@@ -522,7 +521,7 @@ create_append_path(RelOptInfo *rel, List *subpaths)
 	{
 		Path	   *subpath = (Path *) lfirst(l);
 
-		if (l == subpaths)		/* first node? */
+		if (l == list_head(subpaths))		/* first node? */
 			pathnode->path.startup_cost = subpath->startup_cost;
 		pathnode->path.total_cost += subpath->total_cost;
 	}
@@ -608,7 +607,7 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath)
 	Path		agg_path;		/* dummy for result of cost_agg */
 	MemoryContext oldcontext;
 	List	   *sub_targetlist;
-	List	   *l;
+	ListCell   *l;
 	int			numCols;
 
 	/* Caller made a mistake if subpath isn't cheapest_total */
@@ -783,7 +782,7 @@ is_distinct_query(Query *query)
 	 */
 	if (query->groupClause)
 	{
-		List   *gl;
+		ListCell   *gl;
 
 		foreach(gl, query->groupClause)
 		{
@@ -818,7 +817,7 @@ is_distinct_query(Query *query)
 static bool
 hash_safe_tlist(List *tlist)
 {
-	List	   *tl;
+	ListCell   *tl;
 
 	foreach(tl, tlist)
 	{