src/include/storage/itemid.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * itemid.h
   4  *        Standard POSTGRES buffer page item identifier/line pointer definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/itemid.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef ITEMID_H
  15 #define ITEMID_H
  16
  17 /*
  18  * A line pointer on a buffer page.  See buffer page definitions and comments
  19  * for an explanation of how line pointers are used.
  20  *
  21  * In some cases a line pointer is "in use" but does not have any associated
  22  * storage on the page.  By convention, lp_len == 0 in every line pointer
  23  * that does not have storage, independently of its lp_flags state.
  24  */
  25 typedef struct ItemIdData
  26 {
  27         unsigned        lp_off:15,              /* offset to tuple (from start of page) */
  28                                 lp_flags:2,             /* state of line pointer, see below */
  29                                 lp_len:15;              /* byte length of tuple */
  30 } ItemIdData;
  31
  32 typedef ItemIdData *ItemId;
  33
  34 /*
  35  * lp_flags has these possible states.  An UNUSED line pointer is available
  36  * for immediate re-use, the other states are not.
  37  */
  38 #define LP_UNUSED               0               /* unused (should always have lp_len=0) */
  39 #define LP_NORMAL               1               /* used (should always have lp_len>0) */
  40 #define LP_REDIRECT             2               /* HOT redirect (should have lp_len=0) */
  41 #define LP_DEAD                 3               /* dead, may or may not have storage */
  42
  43 /*
  44  * Item offsets and lengths are represented by these types when
  45  * they're not actually stored in an ItemIdData.
  46  */
  47 typedef uint16 ItemOffset;
  48 typedef uint16 ItemLength;
  49
  50
  51 /* ----------------
  52  *              support macros
  53  * ----------------
  54  */
  55
  56 /*
  57  *              ItemIdGetLength
  58  */
  59 #define ItemIdGetLength(itemId) \
  60    ((itemId)->lp_len)
  61
  62 /*
  63  *              ItemIdGetOffset
  64  */
  65 #define ItemIdGetOffset(itemId) \
  66    ((itemId)->lp_off)
  67
  68 /*
  69  *              ItemIdGetFlags
  70  */
  71 #define ItemIdGetFlags(itemId) \
  72    ((itemId)->lp_flags)
  73
  74 /*
  75  *              ItemIdGetRedirect
  76  * In a REDIRECT pointer, lp_off holds offset number for next line pointer
  77  */
  78 #define ItemIdGetRedirect(itemId) \
  79    ((itemId)->lp_off)
  80
  81 /*
  82  * ItemIdIsValid
  83  *              True iff item identifier is valid.
  84  *              This is a pretty weak test, probably useful only in Asserts.
  85  */
  86 #define ItemIdIsValid(itemId)   PointerIsValid(itemId)
  87
  88 /*
  89  * ItemIdIsUsed
  90  *              True iff item identifier is in use.
  91  */
  92 #define ItemIdIsUsed(itemId) \
  93         ((itemId)->lp_flags != LP_UNUSED)
  94
  95 /*
  96  * ItemIdIsNormal
  97  *              True iff item identifier is in state NORMAL.
  98  */
  99 #define ItemIdIsNormal(itemId) \
 100         ((itemId)->lp_flags == LP_NORMAL)
 101
 102 /*
 103  * ItemIdIsRedirected
 104  *              True iff item identifier is in state REDIRECT.
 105  */
 106 #define ItemIdIsRedirected(itemId) \
 107         ((itemId)->lp_flags == LP_REDIRECT)
 108
 109 /*
 110  * ItemIdIsDead
 111  *              True iff item identifier is in state DEAD.
 112  */
 113 #define ItemIdIsDead(itemId) \
 114         ((itemId)->lp_flags == LP_DEAD)
 115
 116 /*
 117  * ItemIdHasStorage
 118  *              True iff item identifier has associated storage.
 119  */
 120 #define ItemIdHasStorage(itemId) \
 121         ((itemId)->lp_len != 0)
 122
 123 /*
 124  * ItemIdSetUnused
 125  *              Set the item identifier to be UNUSED, with no storage.
 126  *              Beware of multiple evaluations of itemId!
 127  */
 128 #define ItemIdSetUnused(itemId) \
 129 ( \
 130         (itemId)->lp_flags = LP_UNUSED, \
 131         (itemId)->lp_off = 0, \
 132         (itemId)->lp_len = 0 \
 133 )
 134
 135 /*
 136  * ItemIdSetNormal
 137  *              Set the item identifier to be NORMAL, with the specified storage.
 138  *              Beware of multiple evaluations of itemId!
 139  */
 140 #define ItemIdSetNormal(itemId, off, len) \
 141 ( \
 142         (itemId)->lp_flags = LP_NORMAL, \
 143         (itemId)->lp_off = (off), \
 144         (itemId)->lp_len = (len) \
 145 )
 146
 147 /*
 148  * ItemIdSetRedirect
 149  *              Set the item identifier to be REDIRECT, with the specified link.
 150  *              Beware of multiple evaluations of itemId!
 151  */
 152 #define ItemIdSetRedirect(itemId, link) \
 153 ( \
 154         (itemId)->lp_flags = LP_REDIRECT, \
 155         (itemId)->lp_off = (link), \
 156         (itemId)->lp_len = 0 \
 157 )
 158
 159 /*
 160  * ItemIdSetDead
 161  *              Set the item identifier to be DEAD, with no storage.
 162  *              Beware of multiple evaluations of itemId!
 163  */
 164 #define ItemIdSetDead(itemId) \
 165 ( \
 166         (itemId)->lp_flags = LP_DEAD, \
 167         (itemId)->lp_off = 0, \
 168         (itemId)->lp_len = 0 \
 169 )
 170
 171 /*
 172  * ItemIdMarkDead
 173  *              Set the item identifier to be DEAD, keeping its existing storage.
 174  *
 175  * Note: in indexes, this is used as if it were a hint-bit mechanism;
 176  * we trust that multiple processors can do this in parallel and get
 177  * the same result.
 178  */
 179 #define ItemIdMarkDead(itemId) \
 180 ( \
 181         (itemId)->lp_flags = LP_DEAD \
 182 )
 183
 184 #endif                                                  /* ITEMID_H */