granicus.if.org Git - postgresql/blob - src/include/storage/itemptr.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * itemptr.h
   4  *        POSTGRES disk item pointer definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/itemptr.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef ITEMPTR_H
  15 #define ITEMPTR_H
  16
  17 #include "storage/block.h"
  18 #include "storage/off.h"
  19
  20 /*
  21  * ItemPointer:
  22  *
  23  * This is a pointer to an item within a disk page of a known file
  24  * (for example, a cross-link from an index to its parent table).
  25  * blkid tells us which block, posid tells us which entry in the linp
  26  * (ItemIdData) array we want.
  27  *
  28  * Note: because there is an item pointer in each tuple header and index
  29  * tuple header on disk, it's very important not to waste space with
  30  * structure padding bytes.  The struct is designed to be six bytes long
  31  * (it contains three int16 fields) but a few compilers will pad it to
  32  * eight bytes unless coerced.  We apply appropriate persuasion where
  33  * possible, and to cope with unpersuadable compilers, we try to use
  34  * "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing
  35  * on-disk sizes.
  36  */
  37 typedef struct ItemPointerData
  38 {
  39         BlockIdData ip_blkid;
  40         OffsetNumber ip_posid;
  41 }
  42
  43 #ifdef __arm__
  44 pg_attribute_packed                     /* Appropriate whack upside the head for ARM */
  45 #endif
  46 ItemPointerData;
  47
  48 #define SizeOfIptrData  \
  49         (offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber))
  50
  51 typedef ItemPointerData *ItemPointer;
  52
  53 /* ----------------
  54  *              support macros
  55  * ----------------
  56  */
  57
  58 /*
  59  * ItemPointerIsValid
  60  *              True iff the disk item pointer is not NULL.
  61  */
  62 #define ItemPointerIsValid(pointer) \
  63         ((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0)))
  64
  65 /*
  66  * ItemPointerGetBlockNumber
  67  *              Returns the block number of a disk item pointer.
  68  */
  69 #define ItemPointerGetBlockNumber(pointer) \
  70 ( \
  71         AssertMacro(ItemPointerIsValid(pointer)), \
  72         BlockIdGetBlockNumber(&(pointer)->ip_blkid) \
  73 )
  74
  75 /*
  76  * ItemPointerGetOffsetNumber
  77  *              Returns the offset number of a disk item pointer.
  78  */
  79 #define ItemPointerGetOffsetNumber(pointer) \
  80 ( \
  81         AssertMacro(ItemPointerIsValid(pointer)), \
  82         (pointer)->ip_posid \
  83 )
  84
  85 /*
  86  * ItemPointerSet
  87  *              Sets a disk item pointer to the specified block and offset.
  88  */
  89 #define ItemPointerSet(pointer, blockNumber, offNum) \
  90 ( \
  91         AssertMacro(PointerIsValid(pointer)), \
  92         BlockIdSet(&((pointer)->ip_blkid), blockNumber), \
  93         (pointer)->ip_posid = offNum \
  94 )
  95
  96 /*
  97  * ItemPointerSetBlockNumber
  98  *              Sets a disk item pointer to the specified block.
  99  */
 100 #define ItemPointerSetBlockNumber(pointer, blockNumber) \
 101 ( \
 102         AssertMacro(PointerIsValid(pointer)), \
 103         BlockIdSet(&((pointer)->ip_blkid), blockNumber) \
 104 )
 105
 106 /*
 107  * ItemPointerSetOffsetNumber
 108  *              Sets a disk item pointer to the specified offset.
 109  */
 110 #define ItemPointerSetOffsetNumber(pointer, offsetNumber) \
 111 ( \
 112         AssertMacro(PointerIsValid(pointer)), \
 113         (pointer)->ip_posid = (offsetNumber) \
 114 )
 115
 116 /*
 117  * ItemPointerCopy
 118  *              Copies the contents of one disk item pointer to another.
 119  *
 120  * Should there ever be padding in an ItemPointer this would need to be handled
 121  * differently as it's used as hash key.
 122  */
 123 #define ItemPointerCopy(fromPointer, toPointer) \
 124 ( \
 125         AssertMacro(PointerIsValid(toPointer)), \
 126         AssertMacro(PointerIsValid(fromPointer)), \
 127         *(toPointer) = *(fromPointer) \
 128 )
 129
 130 /*
 131  * ItemPointerSetInvalid
 132  *              Sets a disk item pointer to be invalid.
 133  */
 134 #define ItemPointerSetInvalid(pointer) \
 135 ( \
 136         AssertMacro(PointerIsValid(pointer)), \
 137         BlockIdSet(&((pointer)->ip_blkid), InvalidBlockNumber), \
 138         (pointer)->ip_posid = InvalidOffsetNumber \
 139 )
 140
 141 /* ----------------
 142  *              externs
 143  * ----------------
 144  */
 145
 146 extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2);
 147 extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2);
 148
 149 #endif   /* ITEMPTR_H */