itemid.h

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/*-------------------------------------------------------------------------
 *
 * itemid.h
 *    Standard POSTGRES buffer page item identifier/line pointer definitions.
 *
 *
 * Portions Copyright (c) 1996-2024, 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
 
/*
 * A line pointer on a buffer page.  See buffer page definitions and comments
 * for an explanation of how line pointers are used.
 *
 * In some cases a line pointer is "in use" but does not have any associated
 * storage on the page.  By convention, lp_len == 0 in every line 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 line 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 offset number for next line 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 */