1 /*-------------------------------------------------------------------------
2  *
3  * itup.h
4  *	  POSTGRES index tuple 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/access/itup.h
11  *
12  *-------------------------------------------------------------------------
13  */
14 #ifndef ITUP_H
15 #define ITUP_H
16 
17 #include "access/tupdesc.h"
18 #include "access/tupmacs.h"
19 #include "storage/bufpage.h"
20 #include "storage/itemptr.h"
21 
22 /*
23  * Index tuple header structure
24  *
25  * All index tuples start with IndexTupleData.  If the HasNulls bit is set,
26  * this is followed by an IndexAttributeBitMapData.  The index attribute
27  * values follow, beginning at a MAXALIGN boundary.
28  *
29  * Note that the space allocated for the bitmap does not vary with the number
30  * of attributes; that is because we don't have room to store the number of
31  * attributes in the header.  Given the MAXALIGN constraint there's no space
32  * savings to be had anyway, for usual values of INDEX_MAX_KEYS.
33  */
34 
35 typedef struct IndexTupleData
36 {
37 	ItemPointerData t_tid;		/* reference TID to heap tuple */
38 
39 	/* ---------------
40 	 * t_info is laid out in the following fashion:
41 	 *
42 	 * 15th (high) bit: has nulls
43 	 * 14th bit: has var-width attributes
44 	 * 13th bit: unused
45 	 * 12-0 bit: size of tuple
46 	 * ---------------
47 	 */
48 
49 	unsigned short t_info;		/* various info about tuple */
50 
51 } IndexTupleData;				/* MORE DATA FOLLOWS AT END OF STRUCT */
52 
53 typedef IndexTupleData *IndexTuple;
54 
55 typedef struct IndexAttributeBitMapData
56 {
57 	bits8		bits[(INDEX_MAX_KEYS + 8 - 1) / 8];
58 }			IndexAttributeBitMapData;
59 
60 typedef IndexAttributeBitMapData * IndexAttributeBitMap;
61 
62 /*
63  * t_info manipulation macros
64  */
65 #define INDEX_SIZE_MASK 0x1FFF
66 /* bit 0x2000 is reserved for index-AM specific usage */
67 #define INDEX_VAR_MASK	0x4000
68 #define INDEX_NULL_MASK 0x8000
69 
70 #define IndexTupleSize(itup)		((Size) (((IndexTuple) (itup))->t_info & INDEX_SIZE_MASK))
71 #define IndexTupleDSize(itup)		((Size) ((itup).t_info & INDEX_SIZE_MASK))
72 #define IndexTupleHasNulls(itup)	((((IndexTuple) (itup))->t_info & INDEX_NULL_MASK))
73 #define IndexTupleHasVarwidths(itup) ((((IndexTuple) (itup))->t_info & INDEX_VAR_MASK))
74 
75 
76 /*
77  * Takes an infomask as argument (primarily because this needs to be usable
78  * at index_form_tuple time so enough space is allocated).
79  */
80 #define IndexInfoFindDataOffset(t_info) \
81 ( \
82 	(!((t_info) & INDEX_NULL_MASK)) ? \
83 	( \
84 		(Size)MAXALIGN(sizeof(IndexTupleData)) \
85 	) \
86 	: \
87 	( \
88 		(Size)MAXALIGN(sizeof(IndexTupleData) + sizeof(IndexAttributeBitMapData)) \
89 	) \
90 )
91 
92 /* ----------------
93  *		index_getattr
94  *
95  *		This gets called many times, so we macro the cacheable and NULL
96  *		lookups, and call nocache_index_getattr() for the rest.
97  *
98  * ----------------
99  */
100 #define index_getattr(tup, attnum, tupleDesc, isnull) \
101 ( \
102 	AssertMacro(PointerIsValid(isnull) && (attnum) > 0), \
103 	*(isnull) = false, \
104 	!IndexTupleHasNulls(tup) ? \
105 	( \
106 		(tupleDesc)->attrs[(attnum)-1]->attcacheoff >= 0 ? \
107 		( \
108 			fetchatt((tupleDesc)->attrs[(attnum)-1], \
109 			(char *) (tup) + IndexInfoFindDataOffset((tup)->t_info) \
110 			+ (tupleDesc)->attrs[(attnum)-1]->attcacheoff) \
111 		) \
112 		: \
113 			nocache_index_getattr((tup), (attnum), (tupleDesc)) \
114 	) \
115 	: \
116 	( \
117 		(att_isnull((attnum)-1, (char *)(tup) + sizeof(IndexTupleData))) ? \
118 		( \
119 			*(isnull) = true, \
120 			(Datum)NULL \
121 		) \
122 		: \
123 		( \
124 			nocache_index_getattr((tup), (attnum), (tupleDesc)) \
125 		) \
126 	) \
127 )
128 
129 /*
130  * MaxIndexTuplesPerPage is an upper bound on the number of tuples that can
131  * fit on one index page.  An index tuple must have either data or a null
132  * bitmap, so we can safely assume it's at least 1 byte bigger than a bare
133  * IndexTupleData struct.  We arrive at the divisor because each tuple
134  * must be maxaligned, and it must have an associated item pointer.
135  */
136 #define MinIndexTupleSize MAXALIGN(sizeof(IndexTupleData) + 1)
137 #define MaxIndexTuplesPerPage	\
138 	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
139 			(MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))))
140 
141 
142 /* routines in indextuple.c */
143 extern IndexTuple index_form_tuple(TupleDesc tupleDescriptor,
144 				 Datum *values, bool *isnull);
145 extern Datum nocache_index_getattr(IndexTuple tup, int attnum,
146 					  TupleDesc tupleDesc);
147 extern void index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor,
148 				   Datum *values, bool *isnull);
149 extern IndexTuple CopyIndexTuple(IndexTuple source);
150 
151 #endif							/* ITUP_H */
152