Redefine the lp_flags field of item pointers as having four states, rather

than two independent bits (one of which was never used in heap pages anyway,
or at least hadn't been in a very long time).  This gives us flexibility to
add the HOT notions of redirected and dead item pointers without requiring
anything so klugy as magic values of lp_off and lp_len.  The state values
are chosen so that for the states currently in use (pre-HOT) there is no
change in the physical representation.

1 files changed, 114 insertions, 28 deletions

diff --git a/src/include/storage/itemid.h b/src/include/storage/itemid.h
index 63a076550f..2a18f18226 100644
--- a/src/include/storage/itemid.h
+++ b/src/include/storage/itemid.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/itemid.h,v 1.27 2007/01/05 22:19:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/itemid.h,v 1.28 2007/09/12 22:10:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -16,41 +16,36 @@
 
 /*
  * An item pointer (also called line pointer) on a buffer page
+ *
+ * In some cases an item pointer is "in use" but does not have any associated
+ * storage on the page.  By convention, lp_len == 0 in every item pointer
+ * that does not have storage, independently of its lp_flags state.
  */
 typedef struct ItemIdData
-{								/* line pointers */
-	unsigned	lp_off:15,		/* offset to start of tuple */
-				lp_flags:2,		/* flags for tuple */
-				lp_len:15;		/* length of tuple */
+{
+	unsigned	lp_off:15,		/* offset to tuple (from start of page) */
+				lp_flags:2,		/* state of item pointer, see below */
+				lp_len:15;		/* byte length of tuple */
 } ItemIdData;
 
 typedef ItemIdData *ItemId;
 
 /*
- * lp_flags contains these flags:
- */
-#define LP_USED			0x01	/* this line pointer is being used */
-
-#define LP_DELETE		0x02	/* item is to be deleted */
-
-#define ItemIdDeleted(itemId) \
-	(((itemId)->lp_flags & LP_DELETE) != 0)
-
-/*
- * This bit may be passed to PageAddItem together with
- * LP_USED & LP_DELETE bits to specify overwrite mode
+ * lp_flags has these possible states.  An UNUSED line pointer is available
+ * for immediate re-use, the other states are not.
  */
-#define OverwritePageMode	0x10
+#define LP_UNUSED		0		/* unused (should always have lp_len=0) */
+#define LP_NORMAL		1		/* used (should always have lp_len>0) */
+#define LP_REDIRECT		2		/* HOT redirect (should have lp_len=0) */
+#define LP_DEAD			3		/* dead, may or may not have storage */
 
 /*
- * Item offsets, lengths, and flags are represented by these types when
+ * Item offsets and lengths are represented by these types when
  * they're not actually stored in an ItemIdData.
  */
 typedef uint16 ItemOffset;
 typedef uint16 ItemLength;
 
-typedef bits16 ItemIdFlags;
-
 
 /* ----------------
  *		support macros
@@ -76,22 +71,113 @@ typedef bits16 ItemIdFlags;
    ((itemId)->lp_flags)
 
 /*
+ *		ItemIdGetRedirect
+ * In a REDIRECT pointer, lp_off holds the link to the next item pointer
+ */
+#define ItemIdGetRedirect(itemId) \
+   ((itemId)->lp_off)
+
+/*
  * ItemIdIsValid
- *		True iff disk item identifier is valid.
+ *		True iff item identifier is valid.
+ *		This is a pretty weak test, probably useful only in Asserts.
  */
 #define ItemIdIsValid(itemId)	PointerIsValid(itemId)
 
 /*
  * ItemIdIsUsed
- *		True iff disk item identifier is in use.
- *
- * Note:
- *		Assumes disk item identifier is valid.
+ *		True iff item identifier is in use.
  */
 #define ItemIdIsUsed(itemId) \
+	((itemId)->lp_flags != LP_UNUSED)
+
+/*
+ * ItemIdIsNormal
+ *		True iff item identifier is in state NORMAL.
+ */
+#define ItemIdIsNormal(itemId) \
+	((itemId)->lp_flags == LP_NORMAL)
+
+/*
+ * ItemIdIsRedirected
+ *		True iff item identifier is in state REDIRECT.
+ */
+#define ItemIdIsRedirected(itemId) \
+	((itemId)->lp_flags == LP_REDIRECT)
+
+/*
+ * ItemIdIsDead
+ *		True iff item identifier is in state DEAD.
+ */
+#define ItemIdIsDead(itemId) \
+	((itemId)->lp_flags == LP_DEAD)
+
+/*
+ * ItemIdHasStorage
+ *		True iff item identifier has associated storage.
+ */
+#define ItemIdHasStorage(itemId) \
+	((itemId)->lp_len != 0)
+
+/*
+ * ItemIdSetUnused
+ *		Set the item identifier to be UNUSED, with no storage.
+ *		Beware of multiple evaluations of itemId!
+ */
+#define ItemIdSetUnused(itemId) \
+( \
+	(itemId)->lp_flags = LP_UNUSED, \
+	(itemId)->lp_off = 0, \
+	(itemId)->lp_len = 0 \
+)
+
+/*
+ * ItemIdSetNormal
+ *		Set the item identifier to be NORMAL, with the specified storage.
+ *		Beware of multiple evaluations of itemId!
+ */
+#define ItemIdSetNormal(itemId, off, len) \
+( \
+	(itemId)->lp_flags = LP_NORMAL, \
+	(itemId)->lp_off = (off), \
+	(itemId)->lp_len = (len) \
+)
+
+/*
+ * ItemIdSetRedirect
+ *		Set the item identifier to be REDIRECT, with the specified link.
+ *		Beware of multiple evaluations of itemId!
+ */
+#define ItemIdSetRedirect(itemId, link) \
+( \
+	(itemId)->lp_flags = LP_REDIRECT, \
+	(itemId)->lp_off = (link), \
+	(itemId)->lp_len = 0 \
+)
+
+/*
+ * ItemIdSetDead
+ *		Set the item identifier to be DEAD, with no storage.
+ *		Beware of multiple evaluations of itemId!
+ */
+#define ItemIdSetDead(itemId) \
+( \
+	(itemId)->lp_flags = LP_DEAD, \
+	(itemId)->lp_off = 0, \
+	(itemId)->lp_len = 0 \
+)
+
+/*
+ * ItemIdMarkDead
+ *		Set the item identifier to be DEAD, keeping its existing storage.
+ *
+ * Note: in indexes, this is used as if it were a hint-bit mechanism;
+ * we trust that multiple processors can do this in parallel and get
+ * the same result.
+ */
+#define ItemIdMarkDead(itemId) \
 ( \
-	AssertMacro(ItemIdIsValid(itemId)), \
-	(bool) (((itemId)->lp_flags & LP_USED) != 0) \
+	(itemId)->lp_flags = LP_DEAD \
 )
 
 #endif   /* ITEMID_H */