Rename MaxTupleSize to MaxHeapTupleSize to clarify that it's not meant to

describe the maximum size of index tuples (which is typically AM-dependent
anyway); and consequently remove the bogus deduction for "special space"
that was built into it.

Adjust TOAST_TUPLE_THRESHOLD and TOAST_MAX_CHUNK_SIZE to avoid wasting two
bytes per toast chunk, and to ensure that the calculation correctly tracks any
future changes in page header size.  The computation had been inaccurate in a
way that didn't cause any harm except space wastage, but future changes could
have broken it more drastically.

Fix the calculation of BTMaxItemSize, which was formerly computed as 1 byte
more than it could safely be.  This didn't cause any harm in practice because
it's only compared against maxalign'd lengths, but future changes in the size
of page headers or btree special space could have exposed the problem.

initdb forced because of change in TOAST_MAX_CHUNK_SIZE, which alters the
storage of toast tables.

1 files changed, 14 insertions, 6 deletions

diff --git a/src/include/c.h b/src/include/c.h
index 9daa9e4c0e..0774ec7cc1 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/c.h,v 1.217 2007/01/25 03:30:43 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/c.h,v 1.218 2007/02/05 04:22:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -537,12 +537,12 @@ typedef NameData *Name;
 
 /* ----------------
  * Alignment macros: align a length or address appropriately for a given type.
+ * The fooALIGN() macros round up to a multiple of the required alignment,
+ * while the fooALIGN_DOWN() macros round down.  The latter are more useful
+ * for problems like "how many X-sized structures will fit in a page?".
  *
- * There used to be some incredibly crufty platform-dependent hackery here,
- * but now we rely on the configure script to get the info for us. Much nicer.
- *
- * NOTE: TYPEALIGN will not work if ALIGNVAL is not a power of 2.
- * That case seems extremely unlikely to occur in practice, however.
+ * NOTE: TYPEALIGN[_DOWN] will not work if ALIGNVAL is not a power of 2.
+ * That case seems extremely unlikely to be needed in practice, however.
  * ----------------
  */
 
@@ -557,6 +557,14 @@ typedef NameData *Name;
 /* MAXALIGN covers only built-in types, not buffers */
 #define BUFFERALIGN(LEN)		TYPEALIGN(ALIGNOF_BUFFER, (LEN))
 
+#define TYPEALIGN_DOWN(ALIGNVAL,LEN)  \
+	(((long) (LEN)) & ~((long) ((ALIGNVAL) - 1)))
+
+#define SHORTALIGN_DOWN(LEN)	TYPEALIGN_DOWN(ALIGNOF_SHORT, (LEN))
+#define INTALIGN_DOWN(LEN)		TYPEALIGN_DOWN(ALIGNOF_INT, (LEN))
+#define LONGALIGN_DOWN(LEN)		TYPEALIGN_DOWN(ALIGNOF_LONG, (LEN))
+#define DOUBLEALIGN_DOWN(LEN)	TYPEALIGN_DOWN(ALIGNOF_DOUBLE, (LEN))
+#define MAXALIGN_DOWN(LEN)		TYPEALIGN_DOWN(MAXIMUM_ALIGNOF, (LEN))
 
 /* ----------------------------------------------------------------
  *				Section 6:	widely useful macros