Clean up the use of some page-header-access macros: principally, use

SizeOfPageHeaderData instead of sizeof(PageHeaderData) in places where that
makes the code clearer, and avoid casting between Page and PageHeader where
possible.  Zdenek Kotala, with some additional cleanup by Heikki Linnakangas.

I did not apply the parts of the proposed patch that would have resulted in
slightly changing the on-disk format of hash indexes; it seems to me that's
not a win as long as there's any chance of having in-place upgrade for 8.4.

5 files changed, 19 insertions, 24 deletions

diff --git a/src/include/access/hash.h b/src/include/access/hash.h
index 4d8cd79e9a8..0dab2b6ae91 100644
--- a/src/include/access/hash.h
+++ b/src/include/access/hash.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/hash.h,v 1.88 2008/06/19 00:46:05 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/access/hash.h,v 1.89 2008/07/13 20:45:47 tgl Exp $
  *
  * NOTES
  *		modeled after Margo Seltzer's hash implementation for unix.
@@ -166,10 +166,10 @@ typedef HashMetaPageData *HashMetaPage;
  * Maximum size of a hash index item (it's okay to have only one per page)
  */
 #define HashMaxItemSize(page) \
-	(PageGetPageSize(page) - \
-	 sizeof(PageHeaderData) - \
-	 MAXALIGN(sizeof(HashPageOpaqueData)) - \
-	 sizeof(ItemIdData))
+	MAXALIGN_DOWN(PageGetPageSize(page) - \
+				  SizeOfPageHeaderData - \
+				  sizeof(ItemIdData) - \
+				  MAXALIGN(sizeof(HashPageOpaqueData)))
 
 #define HASH_MIN_FILLFACTOR			10
 #define HASH_DEFAULT_FILLFACTOR		75
diff --git a/src/include/access/htup.h b/src/include/access/htup.h
index 7a77d438933..8bfdf26697e 100644
--- a/src/include/access/htup.h
+++ b/src/include/access/htup.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/htup.h,v 1.99 2008/05/12 00:00:53 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/access/htup.h,v 1.100 2008/07/13 20:45:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -362,12 +362,12 @@ do { \
  * other stuff that has to be on a disk page.  Since heap pages use no
  * "special space", there's no deduction for that.
  *
- * NOTE: we do not need to count an ItemId for the tuple because
- * sizeof(PageHeaderData) includes the first ItemId on the page.  But beware
- * of assuming that, say, you can fit 2 tuples of size MaxHeapTupleSize/2
- * on the same page.
+ * NOTE: we allow for the ItemId that must point to the tuple, ensuring that
+ * an otherwise-empty page can indeed hold a tuple of this size.  Because
+ * ItemIds and tuples have different alignment requirements, don't assume that
+ * you can, say, fit 2 tuples of size MaxHeapTupleSize/2 on the same page.
  */
-#define MaxHeapTupleSize  (BLCKSZ - MAXALIGN(sizeof(PageHeaderData)))
+#define MaxHeapTupleSize  (BLCKSZ - MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData)))
 
 /*
  * MaxHeapTuplesPerPage is an upper bound on the number of tuples that can
@@ -381,7 +381,7 @@ do { \
  * require increases in the size of work arrays.
  */
 #define MaxHeapTuplesPerPage	\
-	((int) ((BLCKSZ - offsetof(PageHeaderData, pd_linp)) / \
+	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
 			(MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) + sizeof(ItemIdData))))
 
 /*
diff --git a/src/include/access/itup.h b/src/include/access/itup.h
index eb637b81ea4..ae53accde7c 100644
--- a/src/include/access/itup.h
+++ b/src/include/access/itup.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/itup.h,v 1.49 2008/01/01 19:45:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/itup.h,v 1.50 2008/07/13 20:45:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -134,7 +134,7 @@ typedef IndexAttributeBitMapData *IndexAttributeBitMap;
  * must be maxaligned, and it must have an associated item pointer.
  */
 #define MaxIndexTuplesPerPage	\
-	((int) ((BLCKSZ - offsetof(PageHeaderData, pd_linp)) / \
+	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
 			(MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))))
 
 
diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 9b0e8d0cf77..e0bc10c0642 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.120 2008/06/19 00:46:06 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.121 2008/07/13 20:45:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -113,13 +113,10 @@ typedef struct BTMetaPageData
  *
  * We actually need to be able to fit three items on every page,
  * so restrict any one item to 1/3 the per-page available space.
- *
- * Note: sizeof(PageHeaderData) includes the first ItemId, but we have
- * to allow for 2 more, as well as the end-of-page special space.
  */
 #define BTMaxItemSize(page) \
 	MAXALIGN_DOWN((PageGetPageSize(page) - \
-				   MAXALIGN(sizeof(PageHeaderData) + 2*sizeof(ItemIdData)) - \
+				   MAXALIGN(SizeOfPageHeaderData + 3*sizeof(ItemIdData)) - \
 				   MAXALIGN(sizeof(BTPageOpaqueData))) / 3)
 
 /*
diff --git a/src/include/access/tuptoaster.h b/src/include/access/tuptoaster.h
index 7d1ba7d2f82..a87aee62dfc 100644
--- a/src/include/access/tuptoaster.h
+++ b/src/include/access/tuptoaster.h
@@ -6,7 +6,7 @@
  *
  * Copyright (c) 2000-2008, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.40 2008/06/19 00:46:06 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.41 2008/07/13 20:45:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,10 +46,9 @@
  */
 #define TOAST_TUPLES_PER_PAGE	4
 
-/* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
 #define TOAST_TUPLE_THRESHOLD	\
 	MAXALIGN_DOWN((BLCKSZ - \
-				   MAXALIGN(sizeof(PageHeaderData) + (TOAST_TUPLES_PER_PAGE-1) * sizeof(ItemIdData))) \
+				   MAXALIGN(SizeOfPageHeaderData + TOAST_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
 				  / TOAST_TUPLES_PER_PAGE)
 
 #define TOAST_TUPLE_TARGET		TOAST_TUPLE_THRESHOLD
@@ -73,10 +72,9 @@
  */
 #define EXTERN_TUPLES_PER_PAGE	4		/* tweak only this */
 
-/* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
 #define EXTERN_TUPLE_MAX_SIZE	\
 	MAXALIGN_DOWN((BLCKSZ - \
-				   MAXALIGN(sizeof(PageHeaderData) + (EXTERN_TUPLES_PER_PAGE-1) * sizeof(ItemIdData))) \
+				   MAXALIGN(SizeOfPageHeaderData + EXTERN_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
 				  / EXTERN_TUPLES_PER_PAGE)
 
 #define TOAST_MAX_CHUNK_SIZE	\