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pg_include/storage/itemid.h

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+/*-------------------------------------------------------------------------
+ *
+ * itemid.h
+ *	  Standard POSTGRES buffer page item identifier definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/itemid.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef ITEMID_H
+#define ITEMID_H
+
+/*
+ * 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
+{
+	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 has these possible states.	An UNUSED line pointer is available
+ * for immediate re-use, the other states are not.
+ */
+#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 and lengths are represented by these types when
+ * they're not actually stored in an ItemIdData.
+ */
+typedef uint16 ItemOffset;
+typedef uint16 ItemLength;
+
+
+/* ----------------
+ *		support macros
+ * ----------------
+ */
+
+/*
+ *		ItemIdGetLength
+ */
+#define ItemIdGetLength(itemId) \
+   ((itemId)->lp_len)
+
+/*
+ *		ItemIdGetOffset
+ */
+#define ItemIdGetOffset(itemId) \
+   ((itemId)->lp_off)
+
+/*
+ *		ItemIdGetFlags
+ */
+#define ItemIdGetFlags(itemId) \
+   ((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 item identifier is valid.
+ *		This is a pretty weak test, probably useful only in Asserts.
+ */
+#define ItemIdIsValid(itemId)	PointerIsValid(itemId)
+
+/*
+ * ItemIdIsUsed
+ *		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) \
+( \
+	(itemId)->lp_flags = LP_DEAD \
+)
+
+#endif   /* ITEMID_H */