Install a search tree depth limit in GIN bulk-insert operations, to prevent

them from degrading badly when the input is sorted or nearly so.  In this
scenario the tree is unbalanced to the point of becoming a mere linked list,
so insertions become O(N^2).  The easiest and most safely back-patchable
solution is to stop growing the tree sooner, ie limit the growth of N.  We
might later consider a rebalancing tree algorithm, but it's not clear that
the benefit would be worth the cost and complexity.  Per report from Sergey
Burladyan and an earlier complaint from Heikki.

Back-patch to 8.2; older versions didn't have GIN indexes.

src/backend/access/gin/ginfast.c

@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginfast.c,v 1.1 2009/03/24 20:17:10 tgl Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginfast.c,v 1.2 2009/03/24 22:06:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -751,7 +751,8 @@ ginInsertCleanup(Relation index, GinState *ginstate,
 		 */
 		if (GinPageGetOpaque(page)->rightlink == InvalidBlockNumber ||
 			(GinPageHasFullRow(page) &&
-			   accum.allocatedMemory > maintenance_work_mem * 1024L ) )
+			 (accum.allocatedMemory >= maintenance_work_mem * 1024L ||
+			  accum.maxdepth > GIN_MAX_TREE_DEPTH)))
 		{
 			ItemPointerData    *list;
 			uint32      		nlist;

src/backend/access/gin/gininsert.c

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/gininsert.c,v 1.19 2009/03/24 20:17:11 tgl Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/gininsert.c,v 1.20 2009/03/24 22:06:03 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -245,7 +245,9 @@ ginBuildCallback(Relation index, HeapTuple htup, Datum *values,
 														&htup->t_self);
 
 	/* If we've maxed out our available memory, dump everything to the index */
-	if (buildstate->accum.allocatedMemory >= maintenance_work_mem * 1024L)
+	/* Also dump if the tree seems to be getting too unbalanced */
+	if (buildstate->accum.allocatedMemory >= maintenance_work_mem * 1024L ||
+		buildstate->accum.maxdepth > GIN_MAX_TREE_DEPTH)
 	{
 		ItemPointerData *list;
 		Datum		entry;

src/include/access/gin.h

@@ -4,7 +4,7 @@
  *
  *	Copyright (c) 2006-2009, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.29 2009/03/24 20:17:14 tgl Exp $
+ *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.30 2009/03/24 22:06:03 tgl Exp $
  *--------------------------------------------------------------------------
  */
 #ifndef GIN_H
@@ -26,6 +26,14 @@
 #define GIN_COMPARE_PARTIAL_PROC	   5
 #define GINNProcs					   5
 
+/*
+ * Max depth allowed in search tree during bulk inserts.  This is to keep from
+ * degenerating to O(N^2) behavior when the tree is unbalanced due to sorted
+ * or nearly-sorted input.  (Perhaps it would be better to use a balanced-tree
+ * algorithm, but in common cases that would only add useless overhead.)
+ */
+#define GIN_MAX_TREE_DEPTH 100
+
 /*
  * Page opaque data in a inverted index page.
  *
@@ -434,12 +442,9 @@ extern IndexTuple ginPageGetLinkItup(Buffer buf);
 
 /* gindatapage.c */
 extern int	compareItemPointers(ItemPointer a, ItemPointer b);
-extern void
+extern void MergeItemPointers(ItemPointerData *dst,
-MergeItemPointers(
-				  ItemPointerData *dst,
 				  ItemPointerData *a, uint32 na,
-				  ItemPointerData *b, uint32 nb
+				  ItemPointerData *b, uint32 nb);
-);
 
 extern void GinDataPageAddItem(Page page, void *data, OffsetNumber offset);
 extern void PageDeletePostingItem(Page page, OffsetNumber offset);