PostgreSQL Source Code  git master
block.h
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1 /*-------------------------------------------------------------------------
2  *
3  * block.h
4  * POSTGRES disk block definitions.
5  *
6  *
7  * Portions Copyright (c) 1996-2022, 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  */
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 {
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  ((BlockNumber) (blockNumber) != InvalidBlockNumber)
72 
73 /*
74  * BlockIdIsValid
75  * True iff the block identifier is valid.
76  */
77 #define BlockIdIsValid(blockId) \
78  PointerIsValid(blockId)
79 
80 /*
81  * BlockIdSet
82  * Sets a block identifier to the specified value.
83  */
84 #define BlockIdSet(blockId, blockNumber) \
85 ( \
86  (blockId)->bi_hi = (blockNumber) >> 16, \
87  (blockId)->bi_lo = (blockNumber) & 0xffff \
88 )
89 
90 /*
91  * BlockIdCopy
92  * Copy a block identifier.
93  */
94 #define BlockIdCopy(toBlockId, fromBlockId) \
95 ( \
96  (toBlockId)->bi_hi = (fromBlockId)->bi_hi, \
97  (toBlockId)->bi_lo = (fromBlockId)->bi_lo \
98 )
99 
100 /*
101  * BlockIdEquals
102  * Check for block number equality.
103  */
104 #define BlockIdEquals(blockId1, blockId2) \
105  ((blockId1)->bi_hi == (blockId2)->bi_hi && \
106  (blockId1)->bi_lo == (blockId2)->bi_lo)
107 
108 /*
109  * BlockIdGetBlockNumber
110  * Retrieve the block number from a block identifier.
111  */
112 #define BlockIdGetBlockNumber(blockId) \
113  ((((BlockNumber) (blockId)->bi_hi) << 16) | ((BlockNumber) (blockId)->bi_lo))
114 
115 #endif /* BLOCK_H */
uint32 BlockNumber
Definition: block.h:31
struct BlockIdData BlockIdData
BlockIdData * BlockId
Definition: block.h:59
unsigned short uint16
Definition: c.h:451
unsigned int uint32
Definition: c.h:452
uint16 bi_lo
Definition: block.h:56
uint16 bi_hi
Definition: block.h:55