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/*-------------------------------------------------------------------------
*
* itemid.h
* Standard POSTGRES buffer page item identifier definitions.
*
*
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/itemid.h,v 1.31 2009/01/01 17:24:01 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#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 */
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