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, 38 insertions, 30 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index a68dbf1dca9..c306e4563b9 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.93 2004/04/21 18:24:26 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.94 2004/05/26 04:41:16 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -146,7 +146,7 @@ IndexNext(IndexScanState *node)
 	if (estate->es_evTuple != NULL &&
 		estate->es_evTuple[scanrelid - 1] != NULL)
 	{
-		List	   *qual;
+		ListCell   *qual;
 
 		if (estate->es_evTupleNull[scanrelid - 1])
 			return slot;		/* return empty slot */
@@ -164,7 +164,7 @@ IndexNext(IndexScanState *node)
 			if (ExecQual((List *) lfirst(qual), econtext, false))
 				break;
 		}
-		if (qual == NIL)		/* would not be returned by indices */
+		if (qual == NULL)		/* would not be returned by indices */
 			slot->val = NULL;
 
 		/* Flag for the next call that no more tuples */
@@ -283,11 +283,11 @@ IndexNext(IndexScanState *node)
 				{
 					bool		prev_matches = false;
 					int			prev_index;
-					List	   *qual;
+					ListCell   *qual;
 
 					econtext->ecxt_scantuple = slot;
 					ResetExprContext(econtext);
-					qual = node->indxqualorig;
+					qual = list_head(node->indxqualorig);
 					for (prev_index = 0;
 						 prev_index < node->iss_IndexPtr;
 						 prev_index++)
@@ -641,11 +641,11 @@ IndexScanState *
 ExecInitIndexScan(IndexScan *node, EState *estate)
 {
 	IndexScanState *indexstate;
-	List	   *indxqual;
-	List	   *indxstrategy;
-	List	   *indxsubtype;
-	List	   *indxlossy;
-	List	   *indxid;
+	ListCell   *indxqual;
+	ListCell   *indxstrategy;
+	ListCell   *indxsubtype;
+	ListCell   *indxlossy;
+	ListCell   *indxid_item;
 	int			i;
 	int			numIndices;
 	int			indexPtr;
@@ -719,8 +719,8 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 	/*
 	 * get the index node information
 	 */
-	indxid = node->indxid;
-	numIndices = length(indxid);
+	indxid_item = list_head(node->indxid);
+	numIndices = length(node->indxid);
 	indexPtr = -1;
 
 	CXT1_printf("ExecInitIndexScan: context is %d\n", CurrentMemoryContext);
@@ -745,28 +745,32 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 	/*
 	 * build the index scan keys from the index qualification
 	 */
-	indxqual = node->indxqual;
-	indxstrategy = node->indxstrategy;
-	indxsubtype = node->indxsubtype;
-	indxlossy = node->indxlossy;
+	indxqual = list_head(node->indxqual);
+	indxstrategy = list_head(node->indxstrategy);
+	indxsubtype = list_head(node->indxsubtype);
+	indxlossy = list_head(node->indxlossy);
 	for (i = 0; i < numIndices; i++)
 	{
 		List	   *quals;
 		List	   *strategies;
 		List	   *subtypes;
 		List	   *lossyflags;
+		ListCell   *qual_cell;
+		ListCell   *strategy_cell;
+		ListCell   *subtype_cell;
+		ListCell   *lossyflag_cell;
 		int			n_keys;
 		ScanKey		scan_keys;
 		ExprState **run_keys;
 		int			j;
 
-		quals = lfirst(indxqual);
+		quals = (List *) lfirst(indxqual);
 		indxqual = lnext(indxqual);
-		strategies = lfirst(indxstrategy);
+		strategies = (List *) lfirst(indxstrategy);
 		indxstrategy = lnext(indxstrategy);
-		subtypes = lfirst(indxsubtype);
+		subtypes = (List *) lfirst(indxsubtype);
 		indxsubtype = lnext(indxsubtype);
-		lossyflags = lfirst(indxlossy);
+		lossyflags = (List *) lfirst(indxlossy);
 		indxlossy = lnext(indxlossy);
 		n_keys = length(quals);
 		scan_keys = (n_keys <= 0) ? NULL :
@@ -778,6 +782,10 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 		 * for each opclause in the given qual, convert each qual's
 		 * opclause into a single scan key
 		 */
+		qual_cell = list_head(quals);
+		strategy_cell = list_head(strategies);
+		subtype_cell = list_head(subtypes);
+		lossyflag_cell = list_head(lossyflags);
 		for (j = 0; j < n_keys; j++)
 		{
 			OpExpr	   *clause;			/* one clause of index qual */
@@ -794,14 +802,14 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 			/*
 			 * extract clause information from the qualification
 			 */
-			clause = (OpExpr *) lfirst(quals);
-			quals = lnext(quals);
-			strategy = lfirsti(strategies);
-			strategies = lnext(strategies);
-			subtype = lfirsto(subtypes);
-			subtypes = lnext(subtypes);
-			lossy = lfirsti(lossyflags);
-			lossyflags = lnext(lossyflags);
+			clause = (OpExpr *) lfirst(qual_cell);
+			qual_cell = lnext(qual_cell);
+			strategy = lfirsti(strategy_cell);
+			strategy_cell = lnext(strategy_cell);
+			subtype = lfirsto(subtype_cell);
+			subtype_cell = lnext(subtype_cell);
+			lossy = lfirsti(lossyflag_cell);
+			lossyflag_cell = lnext(lossyflag_cell);
 
 			if (!IsA(clause, OpExpr))
 				elog(ERROR, "indxqual is not an OpExpr");
@@ -972,7 +980,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 	 */
 	for (i = 0; i < numIndices; i++)
 	{
-		Oid			indexOid = lfirsto(indxid);
+		Oid			indexOid = lfirsto(indxid_item);
 
 		indexDescs[i] = index_open(indexOid);
 		scanDescs[i] = index_beginscan(currentRelation,
@@ -980,7 +988,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate)
 									   estate->es_snapshot,
 									   numScanKeys[i],
 									   scanKeys[i]);
-		indxid = lnext(indxid);
+		indxid_item = lnext(indxid_item);
 	}
 
 	indexstate->iss_RelationDescs = indexDescs;