1/*-------------------------------------------------------------------------
2 *
3 * block.h
4 * POSTGRES disk block definitions.
5 *
6 *
7 * Portions Copyright (c) 1996-2019, 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 */
31typedef 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 */
53typedef struct BlockIdData
54{
55 uint16 bi_hi;
56 uint16 bi_lo;
57} BlockIdData;
58
59typedef 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 */
122