diff --git a/src/backend/access/gin/gindatapage.c b/src/backend/access/gin/gindatapage.c
index a872d44880..22199102dd 100644
--- a/src/backend/access/gin/gindatapage.c
+++ b/src/backend/access/gin/gindatapage.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/gindatapage.c,v 1.14 2009/03/24 20:17:10 tgl Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/gindatapage.c,v 1.15 2009/06/06 02:39:40 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -32,10 +32,14 @@ compareItemPointers(ItemPointer a, ItemPointer b)
 }
 
 /*
- * Merge two ordered array of itempointer
+ * Merge two ordered arrays of itempointers, eliminating any duplicates.
+ * Returns the number of items in the result.
+ * Caller is responsible that there is enough space at *dst.
  */
-void
-MergeItemPointers(ItemPointerData *dst, ItemPointerData *a, uint32 na, ItemPointerData *b, uint32 nb)
+uint32
+MergeItemPointers(ItemPointerData *dst,
+				  ItemPointerData *a, uint32 na,
+				  ItemPointerData *b, uint32 nb)
 {
 	ItemPointerData *dptr = dst;
 	ItemPointerData *aptr = a,
@@ -62,6 +66,8 @@ MergeItemPointers(ItemPointerData *dst, ItemPointerData *a, uint32 na, ItemPoint
 
 	while (bptr - b < nb)
 		*dptr++ = *bptr++;
+
+	return dptr - dst;
 }
 
 /*
diff --git a/src/backend/access/gin/ginentrypage.c b/src/backend/access/gin/ginentrypage.c
index e16575bc81..f35994db95 100644
--- a/src/backend/access/gin/ginentrypage.c
+++ b/src/backend/access/gin/ginentrypage.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *			$PostgreSQL: pgsql/src/backend/access/gin/ginentrypage.c,v 1.19 2009/01/01 17:23:34 momjian Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/ginentrypage.c,v 1.20 2009/06/06 02:39:40 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -20,28 +20,33 @@
 #include "utils/rel.h"
 
 /*
- * forms tuple for entry tree. On leaf page, Index tuple has
- * non-traditional layout. Tuple may contain posting list or
- * root blocknumber of posting tree. Macros GinIsPostingTre: (itup) / GinSetPostingTree(itup, blkno)
+ * Form a tuple for entry tree.
+ *
+ * On leaf pages, Index tuple has non-traditional layout. Tuple may contain
+ * posting list or root blocknumber of posting tree.
+ * Macros: GinIsPostingTree(itup) / GinSetPostingTree(itup, blkno)
  * 1) Posting list
- *		- itup->t_info & INDEX_SIZE_MASK contains size of tuple as usual
+ *		- itup->t_info & INDEX_SIZE_MASK contains total size of tuple as usual
  *		- ItemPointerGetBlockNumber(&itup->t_tid) contains original
  *		  size of tuple (without posting list).
- *		  Macroses: GinGetOrigSizePosting(itup) / GinSetOrigSizePosting(itup,n)
+ *		  Macros: GinGetOrigSizePosting(itup) / GinSetOrigSizePosting(itup,n)
  *		- ItemPointerGetOffsetNumber(&itup->t_tid) contains number
- *		  of elements in posting list (number of heap itempointer)
- *		  Macroses: GinGetNPosting(itup) / GinSetNPosting(itup,n)
- *		- After usual part of tuple there is a posting list
+ *		  of elements in posting list (number of heap itempointers)
+ *		  Macros: GinGetNPosting(itup) / GinSetNPosting(itup,n)
+ *		- After standard part of tuple there is a posting list, ie, array
+ *		  of heap itempointers
  *		  Macros: GinGetPosting(itup)
  * 2) Posting tree
  *		- itup->t_info & INDEX_SIZE_MASK contains size of tuple as usual
  *		- ItemPointerGetBlockNumber(&itup->t_tid) contains block number of
  *		  root of posting tree
- *		- ItemPointerGetOffsetNumber(&itup->t_tid) contains magic number GIN_TREE_POSTING
+ *		- ItemPointerGetOffsetNumber(&itup->t_tid) contains magic number
+ *		  GIN_TREE_POSTING, which distinguishes this from posting-list case
  *
- * Storage of attributes of tuple are different for single and multicolumn index.
- * For single-column index tuple stores only value to be indexed and for
- * multicolumn variant it stores two attributes: column number of value and value. 
+ * Attributes of an index tuple are different for single and multicolumn index.
+ * For single-column case, index tuple stores only value to be indexed.
+ * For multicolumn case, it stores two attributes: column number of value
+ * and value. 
  */
 IndexTuple
 GinFormTuple(GinState *ginstate, OffsetNumber attnum, Datum key, ItemPointerData *ipd, uint32 nipd)
@@ -89,6 +94,28 @@ GinFormTuple(GinState *ginstate, OffsetNumber attnum, Datum key, ItemPointerData
 	return itup;
 }
 
+/*
+ * Sometimes we reduce the number of posting list items in a tuple after
+ * having built it with GinFormTuple.  This function adjusts the size
+ * fields to match.
+ */
+void
+GinShortenTuple(IndexTuple itup, uint32 nipd)
+{
+	uint32		newsize;
+
+	Assert(nipd <= GinGetNPosting(itup));
+
+	newsize = MAXALIGN(SHORTALIGN(GinGetOrigSizePosting(itup)) + sizeof(ItemPointerData) * nipd);
+
+	Assert(newsize <= (itup->t_info & INDEX_SIZE_MASK));
+
+	itup->t_info &= ~INDEX_SIZE_MASK;
+	itup->t_info |= newsize;
+
+	GinSetNPosting(itup, nipd);
+}
+
 /*
  * Entry tree is a "static", ie tuple never deletes from it,
  * so we don't use right bound, we use rightest key instead.
diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index f6a348eb85..ef3d4bbb03 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/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 1.20 2009/03/24 22:06:03 tgl Exp $
+ *			$PostgreSQL: pgsql/src/backend/access/gin/gininsert.c,v 1.21 2009/06/06 02:39:40 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -102,17 +102,19 @@ addItemPointersToTuple(Relation index, GinState *ginstate, GinBtreeStack *stack,
 {
 	Datum			key = gin_index_getattr(ginstate, old);
 	OffsetNumber	attnum = gintuple_get_attrnum(ginstate, old);
-	IndexTuple		res = GinFormTuple(ginstate, attnum, key, NULL, nitem + GinGetNPosting(old));
+	IndexTuple		res = GinFormTuple(ginstate, attnum, key,
+									   NULL, nitem + GinGetNPosting(old));
 
 	if (res)
 	{
 		/* good, small enough */
-		MergeItemPointers(GinGetPosting(res),
-						  GinGetPosting(old), GinGetNPosting(old),
-						  items, nitem
-			);
+		uint32 newnitem;
 
-		GinSetNPosting(res, nitem + GinGetNPosting(old));
+		newnitem = MergeItemPointers(GinGetPosting(res),
+									 GinGetPosting(old), GinGetNPosting(old),
+									 items, nitem);
+		/* merge might have eliminated some duplicate items */
+		GinShortenTuple(res, newnitem);
 	}
 	else
 	{
diff --git a/src/include/access/gin.h b/src/include/access/gin.h
index 49a14b6290..366fc370b0 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 1.32 2009/06/05 18:50:47 tgl Exp $
+ *	$PostgreSQL: pgsql/src/include/access/gin.h,v 1.33 2009/06/06 02:39:40 tgl Exp $
  *--------------------------------------------------------------------------
  */
 #ifndef GIN_H
@@ -435,6 +435,7 @@ extern void findParents(GinBtree btree, GinBtreeStack *stack, BlockNumber rootBl
 /* ginentrypage.c */
 extern IndexTuple GinFormTuple(GinState *ginstate, OffsetNumber attnum, Datum key,
 										ItemPointerData *ipd, uint32 nipd);
+extern void GinShortenTuple(IndexTuple itup, uint32 nipd);
 extern void prepareEntryScan(GinBtree btree, Relation index, OffsetNumber attnum,
 								Datum value, GinState *ginstate);
 extern void entryFillRoot(GinBtree btree, Buffer root, Buffer lbuf, Buffer rbuf);
@@ -442,7 +443,7 @@ extern IndexTuple ginPageGetLinkItup(Buffer buf);
 
 /* gindatapage.c */
 extern int	compareItemPointers(ItemPointer a, ItemPointer b);
-extern void MergeItemPointers(ItemPointerData *dst,
+extern uint32 MergeItemPointers(ItemPointerData *dst,
 				  ItemPointerData *a, uint32 na,
 				  ItemPointerData *b, uint32 nb);