src/include/storage/itemid.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * itemid.h
   4  *        Standard POSTGRES buffer page item identifier definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * $PostgreSQL$
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef ITEMID_H
  15 #define ITEMID_H
  16
  17 /*
  18  * An item pointer (also called line pointer) on a buffer page
  19  *
  20  * In some cases an item pointer is "in use" but does not have any associated
  21  * storage on the page.  By convention, lp_len == 0 in every item pointer
  22  * that does not have storage, independently of its lp_flags state.
  23  */
  24 typedef struct ItemIdData
  25 {
  26         unsigned        lp_off:15,              /* offset to tuple (from start of page) */
  27                                 lp_flags:2,             /* state of item pointer, see below */
  28                                 lp_len:15;              /* byte length of tuple */
  29 } ItemIdData;
  30
  31 typedef ItemIdData *ItemId;
  32
  33 /*
  34  * lp_flags has these possible states.  An UNUSED line pointer is available
  35  * for immediate re-use, the other states are not.
  36  */
  37 #define LP_UNUSED               0               /* unused (should always have lp_len=0) */
  38 #define LP_NORMAL               1               /* used (should always have lp_len>0) */
  39 #define LP_REDIRECT             2               /* HOT redirect (should have lp_len=0) */
  40 #define LP_DEAD                 3               /* dead, may or may not have storage */
  41
  42 /*
  43  * Item offsets and lengths are represented by these types when
  44  * they're not actually stored in an ItemIdData.
  45  */
  46 typedef uint16 ItemOffset;
  47 typedef uint16 ItemLength;
  48
  49
  50 /* ----------------
  51  *              support macros
  52  * ----------------
  53  */
  54
  55 /*
  56  *              ItemIdGetLength
  57  */
  58 #define ItemIdGetLength(itemId) \
  59    ((itemId)->lp_len)
  60
  61 /*
  62  *              ItemIdGetOffset
  63  */
  64 #define ItemIdGetOffset(itemId) \
  65    ((itemId)->lp_off)
  66
  67 /*
  68  *              ItemIdGetFlags
  69  */
  70 #define ItemIdGetFlags(itemId) \
  71    ((itemId)->lp_flags)
  72
  73 /*
  74  *              ItemIdGetRedirect
  75  * In a REDIRECT pointer, lp_off holds the link to the next item pointer
  76  */
  77 #define ItemIdGetRedirect(itemId) \
  78    ((itemId)->lp_off)
  79
  80 /*
  81  * ItemIdIsValid
  82  *              True iff item identifier is valid.
  83  *              This is a pretty weak test, probably useful only in Asserts.
  84  */
  85 #define ItemIdIsValid(itemId)   PointerIsValid(itemId)
  86
  87 /*
  88  * ItemIdIsUsed
  89  *              True iff item identifier is in use.
  90  */
  91 #define ItemIdIsUsed(itemId) \
  92         ((itemId)->lp_flags != LP_UNUSED)
  93
  94 /*
  95  * ItemIdIsNormal
  96  *              True iff item identifier is in state NORMAL.
  97  */
  98 #define ItemIdIsNormal(itemId) \
  99         ((itemId)->lp_flags == LP_NORMAL)
 100
 101 /*
 102  * ItemIdIsRedirected
 103  *              True iff item identifier is in state REDIRECT.
 104  */
 105 #define ItemIdIsRedirected(itemId) \
 106         ((itemId)->lp_flags == LP_REDIRECT)
 107
 108 /*
 109  * ItemIdIsDead
 110  *              True iff item identifier is in state DEAD.
 111  */
 112 #define ItemIdIsDead(itemId) \
 113         ((itemId)->lp_flags == LP_DEAD)
 114
 115 /*
 116  * ItemIdHasStorage
 117  *              True iff item identifier has associated storage.
 118  */
 119 #define ItemIdHasStorage(itemId) \
 120         ((itemId)->lp_len != 0)
 121
 122 /*
 123  * ItemIdSetUnused
 124  *              Set the item identifier to be UNUSED, with no storage.
 125  *              Beware of multiple evaluations of itemId!
 126  */
 127 #define ItemIdSetUnused(itemId) \
 128 ( \
 129         (itemId)->lp_flags = LP_UNUSED, \
 130         (itemId)->lp_off = 0, \
 131         (itemId)->lp_len = 0 \
 132 )
 133
 134 /*
 135  * ItemIdSetNormal
 136  *              Set the item identifier to be NORMAL, with the specified storage.
 137  *              Beware of multiple evaluations of itemId!
 138  */
 139 #define ItemIdSetNormal(itemId, off, len) \
 140 ( \
 141         (itemId)->lp_flags = LP_NORMAL, \
 142         (itemId)->lp_off = (off), \
 143         (itemId)->lp_len = (len) \
 144 )
 145
 146 /*
 147  * ItemIdSetRedirect
 148  *              Set the item identifier to be REDIRECT, with the specified link.
 149  *              Beware of multiple evaluations of itemId!
 150  */
 151 #define ItemIdSetRedirect(itemId, link) \
 152 ( \
 153         (itemId)->lp_flags = LP_REDIRECT, \
 154         (itemId)->lp_off = (link), \
 155         (itemId)->lp_len = 0 \
 156 )
 157
 158 /*
 159  * ItemIdSetDead
 160  *              Set the item identifier to be DEAD, with no storage.
 161  *              Beware of multiple evaluations of itemId!
 162  */
 163 #define ItemIdSetDead(itemId) \
 164 ( \
 165         (itemId)->lp_flags = LP_DEAD, \
 166         (itemId)->lp_off = 0, \
 167         (itemId)->lp_len = 0 \
 168 )
 169
 170 /*
 171  * ItemIdMarkDead
 172  *              Set the item identifier to be DEAD, keeping its existing storage.
 173  *
 174  * Note: in indexes, this is used as if it were a hint-bit mechanism;
 175  * we trust that multiple processors can do this in parallel and get
 176  * the same result.
 177  */
 178 #define ItemIdMarkDead(itemId) \
 179 ( \
 180         (itemId)->lp_flags = LP_DEAD \
 181 )
 182
 183 #endif   /* ITEMID_H */