src/include/storage/block.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * block.h
   4  *        POSTGRES disk block 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/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 macros
  63  * ----------------
  64  */
  65
  66 /*
  67  * BlockNumberIsValid
  68  *              True iff blockNumber is valid.
  69  */
  70 #define BlockNumberIsValid(blockNumber) \
  71         ((bool) ((BlockNumber) (blockNumber) != InvalidBlockNumber))
  72
  73 /*
  74  * BlockIdIsValid
  75  *              True iff the block identifier is valid.
  76  */
  77 #define BlockIdIsValid(blockId) \
  78         ((bool) PointerIsValid(blockId))
  79
  80 /*
  81  * BlockIdSet
  82  *              Sets a block identifier to the specified value.
  83  */
  84 #define BlockIdSet(blockId, blockNumber) \
  85 ( \
  86         AssertMacro(PointerIsValid(blockId)), \
  87         (blockId)->bi_hi = (blockNumber) >> 16, \
  88         (blockId)->bi_lo = (blockNumber) & 0xffff \
  89 )
  90
  91 /*
  92  * BlockIdCopy
  93  *              Copy a block identifier.
  94  */
  95 #define BlockIdCopy(toBlockId, fromBlockId) \
  96 ( \
  97         AssertMacro(PointerIsValid(toBlockId)), \
  98         AssertMacro(PointerIsValid(fromBlockId)), \
  99         (toBlockId)->bi_hi = (fromBlockId)->bi_hi, \
 100         (toBlockId)->bi_lo = (fromBlockId)->bi_lo \
 101 )
 102
 103 /*
 104  * BlockIdEquals
 105  *              Check for block number equality.
 106  */
 107 #define BlockIdEquals(blockId1, blockId2) \
 108         ((blockId1)->bi_hi == (blockId2)->bi_hi && \
 109          (blockId1)->bi_lo == (blockId2)->bi_lo)
 110
 111 /*
 112  * BlockIdGetBlockNumber
 113  *              Retrieve the block number from a block identifier.
 114  */
 115 #define BlockIdGetBlockNumber(blockId) \
 116 ( \
 117         AssertMacro(BlockIdIsValid(blockId)), \
 118         (BlockNumber) (((blockId)->bi_hi << 16) | ((uint16) (blockId)->bi_lo)) \
 119 )
 120
 121 #endif                                                  /* BLOCK_H */