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block.h
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1 /*-------------------------------------------------------------------------
2  *
3  * block.h
4  * POSTGRES disk block definitions.
5  *
6  *
7  * Portions Copyright (c) 1996-2017, 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 buf.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 {
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 */
uint32 BlockNumber
Definition: block.h:31
uint16 bi_hi
Definition: block.h:55
unsigned short uint16
Definition: c.h:257
unsigned int uint32
Definition: c.h:258
BlockIdData * BlockId
Definition: block.h:59
struct BlockIdData BlockIdData
uint16 bi_lo
Definition: block.h:56