src/include/storage/block.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * block.h
   4  *        POSTGRES disk block definitions.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/block.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef BLOCK_H
  15 #define BLOCK_H
  16
  17 /*
  18  * BlockNumber:
  19  *
  20  * each data file (heap or index) is divided into postgres disk blocks
  21  * (which may be thought of as the unit of i/o -- a postgres buffer
  22  * contains exactly one disk block).  the blocks are numbered
  23  * sequentially, 0 to 0xFFFFFFFE.
  24  *
  25  * InvalidBlockNumber is the same thing as P_NEW in bufmgr.h.
  26  *
  27  * the access methods, the buffer manager and the storage manager are
  28  * more or less the only pieces of code that should be accessing disk
  29  * blocks directly.
  30  */
  31 typedef uint32 BlockNumber;
  32
  33 #define InvalidBlockNumber              ((BlockNumber) 0xFFFFFFFF)
  34
  35 #define MaxBlockNumber                  ((BlockNumber) 0xFFFFFFFE)
  36
  37 /*
  38  * BlockId:
  39  *
  40  * this is a storage type for BlockNumber.  in other words, this type
  41  * is used for on-disk structures (e.g., in HeapTupleData) whereas
  42  * BlockNumber is the type on which calculations are performed (e.g.,
  43  * in access method code).
  44  *
  45  * there doesn't appear to be any reason to have separate types except
  46  * for the fact that BlockIds can be SHORTALIGN'd (and therefore any
  47  * structures that contains them, such as ItemPointerData, can also be
  48  * SHORTALIGN'd).  this is an important consideration for reducing the
  49  * space requirements of the line pointer (ItemIdData) array on each
  50  * page and the header of each heap or index tuple, so it doesn't seem
  51  * wise to change this without good reason.
  52  */
  53 typedef struct BlockIdData
  54 {
  55         uint16          bi_hi;
  56         uint16          bi_lo;
  57 } BlockIdData;
  58
  59 typedef BlockIdData *BlockId;   /* block identifier */
  60
  61 /* ----------------
  62  *              support functions
  63  * ----------------
  64  */
  65
  66 /*
  67  * BlockNumberIsValid
  68  *              True iff blockNumber is valid.
  69  */
  70 static inline bool
  71 BlockNumberIsValid(BlockNumber blockNumber)
  72 {
  73         return blockNumber != InvalidBlockNumber;
  74 }
  75
  76 /*
  77  * BlockIdSet
  78  *              Sets a block identifier to the specified value.
  79  */
  80 static inline void
  81 BlockIdSet(BlockIdData *blockId, BlockNumber blockNumber)
  82 {
  83         blockId->bi_hi = blockNumber >> 16;
  84         blockId->bi_lo = blockNumber & 0xffff;
  85 }
  86
  87 /*
  88  * BlockIdEquals
  89  *              Check for block number equality.
  90  */
  91 static inline bool
  92 BlockIdEquals(const BlockIdData *blockId1, const BlockIdData *blockId2)
  93 {
  94         return (blockId1->bi_hi == blockId2->bi_hi &&
  95                         blockId1->bi_lo == blockId2->bi_lo);
  96 }
  97
  98 /*
  99  * BlockIdGetBlockNumber
 100  *              Retrieve the block number from a block identifier.
 101  */
 102 static inline BlockNumber
 103 BlockIdGetBlockNumber(const BlockIdData *blockId)
 104 {
 105         return (((BlockNumber) blockId->bi_hi) << 16) | ((BlockNumber) blockId->bi_lo);
 106 }
 107
 108 #endif                                                  /* BLOCK_H */