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.

1 files changed, 11 insertions, 6 deletions

diff --git a/src/include/access/gin.h b/src/include/access/gin.h
index f0f45bc5e8a..c591c53638c 100644
--- a/src/include/access/gin.h
+++ b/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
@@ -27,6 +27,14 @@
 #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.
  *
  * Note: GIN does not include a page ID word as do the other index types.
@@ -434,12 +442,9 @@ extern IndexTuple ginPageGetLinkItup(Buffer buf);
 
 /* gindatapage.c */
 extern int	compareItemPointers(ItemPointer a, ItemPointer b);
-extern void
-MergeItemPointers(
-				  ItemPointerData *dst,
+extern void 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);