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gist.h
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1 /*-------------------------------------------------------------------------
2  *
3  * gist.h
4  * The public API for GiST indexes. This API is exposed to
5  * individuals implementing GiST indexes, so backward-incompatible
6  * changes should be made with care.
7  *
8  *
9  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
10  * Portions Copyright (c) 1994, Regents of the University of California
11  *
12  * src/include/access/gist.h
13  *
14  *-------------------------------------------------------------------------
15  */
16 #ifndef GIST_H
17 #define GIST_H
18 
19 #include "access/itup.h"
20 #include "access/transam.h"
21 #include "access/xlog.h"
22 #include "access/xlogdefs.h"
23 #include "storage/block.h"
24 #include "storage/bufpage.h"
25 #include "utils/relcache.h"
26 
27 /*
28  * amproc indexes for GiST indexes.
29  */
30 #define GIST_CONSISTENT_PROC 1
31 #define GIST_UNION_PROC 2
32 #define GIST_COMPRESS_PROC 3
33 #define GIST_DECOMPRESS_PROC 4
34 #define GIST_PENALTY_PROC 5
35 #define GIST_PICKSPLIT_PROC 6
36 #define GIST_EQUAL_PROC 7
37 #define GIST_DISTANCE_PROC 8
38 #define GIST_FETCH_PROC 9
39 #define GIST_OPTIONS_PROC 10
40 #define GIST_SORTSUPPORT_PROC 11
41 #define GISTNProcs 11
42 
43 /*
44  * Page opaque data in a GiST index page.
45  */
46 #define F_LEAF (1 << 0) /* leaf page */
47 #define F_DELETED (1 << 1) /* the page has been deleted */
48 #define F_TUPLES_DELETED (1 << 2) /* some tuples on the page were
49  * deleted */
50 #define F_FOLLOW_RIGHT (1 << 3) /* page to the right has no downlink */
51 #define F_HAS_GARBAGE (1 << 4) /* some tuples on the page are dead,
52  * but not deleted yet */
53 
54 /*
55  * NSN (node sequence number) is a special-purpose LSN which is stored on each
56  * index page in GISTPageOpaqueData and updated only during page splits. By
57  * recording the parent's LSN in GISTSearchItem.parentlsn, it is possible to
58  * detect concurrent child page splits by checking if parentlsn < child's NSN,
59  * and handle them properly. The child page's LSN is insufficient for this
60  * purpose since it is updated for every page change.
61  */
63 
64 /*
65  * A fake LSN / NSN value used during index builds. Must be smaller than any
66  * real or fake (unlogged) LSN generated after the index build completes so
67  * that all splits are considered complete.
68  */
69 #define GistBuildLSN ((XLogRecPtr) 1)
70 
71 /*
72  * For on-disk compatibility with pre-9.3 servers, NSN is stored as two
73  * 32-bit fields on disk, same as LSNs.
74  */
76 
77 typedef struct GISTPageOpaqueData
78 {
79  PageGistNSN nsn; /* this value must change on page split */
80  BlockNumber rightlink; /* next page if any */
81  uint16 flags; /* see bit definitions above */
82  uint16 gist_page_id; /* for identification of GiST indexes */
84 
86 
87 /*
88  * Maximum possible sizes for GiST index tuple and index key. Calculation is
89  * based on assumption that GiST page should fit at least 4 tuples. In theory,
90  * GiST index can be functional when page can fit 3 tuples. But that seems
91  * rather inefficient, so we use a bit conservative estimate.
92  *
93  * The maximum size of index key is true for unicolumn index. Therefore, this
94  * estimation should be used to figure out which maximum size of GiST index key
95  * makes sense at all. For multicolumn indexes, user might be able to tune
96  * key size using opclass parameters.
97  */
98 #define GISTMaxIndexTupleSize \
99  MAXALIGN_DOWN((BLCKSZ - SizeOfPageHeaderData - sizeof(GISTPageOpaqueData)) / \
100  4 - sizeof(ItemIdData))
101 
102 #define GISTMaxIndexKeySize \
103  (GISTMaxIndexTupleSize - MAXALIGN(sizeof(IndexTupleData)))
104 
105 /*
106  * The page ID is for the convenience of pg_filedump and similar utilities,
107  * which otherwise would have a hard time telling pages of different index
108  * types apart. It should be the last 2 bytes on the page. This is more or
109  * less "free" due to alignment considerations.
110  */
111 #define GIST_PAGE_ID 0xFF81
112 
113 /*
114  * This is the Split Vector to be returned by the PickSplit method.
115  * PickSplit should fill the indexes of tuples to go to the left side into
116  * spl_left[], and those to go to the right into spl_right[] (note the method
117  * is responsible for palloc'ing both of these arrays!). The tuple counts
118  * go into spl_nleft/spl_nright, and spl_ldatum/spl_rdatum must be set to
119  * the union keys for each side.
120  *
121  * If spl_ldatum_exists and spl_rdatum_exists are true, then we are performing
122  * a "secondary split" using a non-first index column. In this case some
123  * decisions have already been made about a page split, and the set of tuples
124  * being passed to PickSplit is just the tuples about which we are undecided.
125  * spl_ldatum/spl_rdatum then contain the union keys for the tuples already
126  * chosen to go left or right. Ideally the PickSplit method should take those
127  * keys into account while deciding what to do with the remaining tuples, ie
128  * it should try to "build out" from those unions so as to minimally expand
129  * them. If it does so, it should union the given tuples' keys into the
130  * existing spl_ldatum/spl_rdatum values rather than just setting those values
131  * from scratch, and then set spl_ldatum_exists/spl_rdatum_exists to false to
132  * show it has done this.
133  *
134  * If the PickSplit method fails to clear spl_ldatum_exists/spl_rdatum_exists,
135  * the core GiST code will make its own decision about how to merge the
136  * secondary-split results with the previously-chosen tuples, and will then
137  * recompute the union keys from scratch. This is a workable though often not
138  * optimal approach.
139  */
140 typedef struct GIST_SPLITVEC
141 {
142  OffsetNumber *spl_left; /* array of entries that go left */
143  int spl_nleft; /* size of this array */
144  Datum spl_ldatum; /* Union of keys in spl_left */
145  bool spl_ldatum_exists; /* true, if spl_ldatum already exists. */
146 
147  OffsetNumber *spl_right; /* array of entries that go right */
148  int spl_nright; /* size of the array */
149  Datum spl_rdatum; /* Union of keys in spl_right */
150  bool spl_rdatum_exists; /* true, if spl_rdatum already exists. */
151 } GIST_SPLITVEC;
152 
153 /*
154  * An entry on a GiST node. Contains the key, as well as its own
155  * location (rel,page,offset) which can supply the matching pointer.
156  * leafkey is a flag to tell us if the entry is in a leaf node.
157  */
158 typedef struct GISTENTRY
159 {
164  bool leafkey;
165 } GISTENTRY;
166 
167 #define GistPageGetOpaque(page) ( (GISTPageOpaque) PageGetSpecialPointer(page) )
168 
169 #define GistPageIsLeaf(page) ( GistPageGetOpaque(page)->flags & F_LEAF)
170 #define GIST_LEAF(entry) (GistPageIsLeaf((entry)->page))
171 
172 #define GistPageIsDeleted(page) ( GistPageGetOpaque(page)->flags & F_DELETED)
173 
174 #define GistTuplesDeleted(page) ( GistPageGetOpaque(page)->flags & F_TUPLES_DELETED)
175 #define GistMarkTuplesDeleted(page) ( GistPageGetOpaque(page)->flags |= F_TUPLES_DELETED)
176 #define GistClearTuplesDeleted(page) ( GistPageGetOpaque(page)->flags &= ~F_TUPLES_DELETED)
177 
178 #define GistPageHasGarbage(page) ( GistPageGetOpaque(page)->flags & F_HAS_GARBAGE)
179 #define GistMarkPageHasGarbage(page) ( GistPageGetOpaque(page)->flags |= F_HAS_GARBAGE)
180 #define GistClearPageHasGarbage(page) ( GistPageGetOpaque(page)->flags &= ~F_HAS_GARBAGE)
181 
182 #define GistFollowRight(page) ( GistPageGetOpaque(page)->flags & F_FOLLOW_RIGHT)
183 #define GistMarkFollowRight(page) ( GistPageGetOpaque(page)->flags |= F_FOLLOW_RIGHT)
184 #define GistClearFollowRight(page) ( GistPageGetOpaque(page)->flags &= ~F_FOLLOW_RIGHT)
185 
186 #define GistPageGetNSN(page) ( PageXLogRecPtrGet(GistPageGetOpaque(page)->nsn))
187 #define GistPageSetNSN(page, val) ( PageXLogRecPtrSet(GistPageGetOpaque(page)->nsn, val))
188 
189 
190 /*
191  * On a deleted page, we store this struct. A deleted page doesn't contain any
192  * tuples, so we don't use the normal page layout with line pointers. Instead,
193  * this struct is stored right after the standard page header. pd_lower points
194  * to the end of this struct. If we add fields to this struct in the future, we
195  * can distinguish the old and new formats by pd_lower.
196  */
198 {
199  /* last xid which could see the page in a scan */
202 
203 static inline void
205 {
206  Assert(PageIsEmpty(page));
207 
208  GistPageGetOpaque(page)->flags |= F_DELETED;
209  ((PageHeader) page)->pd_lower = MAXALIGN(SizeOfPageHeaderData) + sizeof(GISTDeletedPageContents);
210 
211  ((GISTDeletedPageContents *) PageGetContents(page))->deleteXid = deletexid;
212 }
213 
214 static inline FullTransactionId
216 {
217  Assert(GistPageIsDeleted(page));
218 
219  /* Is the deleteXid field present? */
220  if (((PageHeader) page)->pd_lower >= MAXALIGN(SizeOfPageHeaderData) +
221  offsetof(GISTDeletedPageContents, deleteXid) + sizeof(FullTransactionId))
222  {
223  return ((GISTDeletedPageContents *) PageGetContents(page))->deleteXid;
224  }
225  else
227 }
228 
229 /*
230  * Vector of GISTENTRY structs; user-defined methods union and picksplit
231  * take it as one of their arguments
232  */
233 typedef struct
234 {
235  int32 n; /* number of elements */
238 
239 #define GEVHDRSZ (offsetof(GistEntryVector, vector))
240 
241 /*
242  * macro to initialize a GISTENTRY
243  */
244 #define gistentryinit(e, k, r, pg, o, l) \
245  do { (e).key = (k); (e).rel = (r); (e).page = (pg); \
246  (e).offset = (o); (e).leafkey = (l); } while (0)
247 
248 #endif /* GIST_H */
Relation rel
Definition: gist.h:161
bool spl_rdatum_exists
Definition: gist.h:150
#define GistPageIsDeleted(page)
Definition: gist.h:172
#define PageIsEmpty(page)
Definition: bufpage.h:222
struct GIST_SPLITVEC GIST_SPLITVEC
OffsetNumber * spl_left
Definition: gist.h:142
Datum spl_rdatum
Definition: gist.h:149
int32 n
Definition: gist.h:235
#define FLEXIBLE_ARRAY_MEMBER
Definition: c.h:350
bool spl_ldatum_exists
Definition: gist.h:145
uint32 BlockNumber
Definition: block.h:31
int spl_nleft
Definition: gist.h:143
#define SizeOfPageHeaderData
Definition: bufpage.h:216
signed int int32
Definition: c.h:429
uint16 OffsetNumber
Definition: off.h:24
Page page
Definition: gist.h:162
uint16 gist_page_id
Definition: gist.h:82
PageXLogRecPtr PageGistNSN
Definition: gist.h:75
unsigned short uint16
Definition: c.h:440
struct GISTENTRY GISTENTRY
#define FirstNormalTransactionId
Definition: transam.h:34
int spl_nright
Definition: gist.h:148
Datum key
Definition: gist.h:160
struct GISTPageOpaqueData GISTPageOpaqueData
uint16 flags
Definition: gist.h:81
static void GistPageSetDeleted(Page page, FullTransactionId deletexid)
Definition: gist.h:204
bool leafkey
Definition: gist.h:164
FullTransactionId deleteXid
Definition: gist.h:200
#define PageGetContents(page)
Definition: bufpage.h:246
uintptr_t Datum
Definition: postgres.h:411
#define GistPageGetOpaque(page)
Definition: gist.h:167
PageHeaderData * PageHeader
Definition: bufpage.h:166
struct GISTDeletedPageContents GISTDeletedPageContents
Datum spl_ldatum
Definition: gist.h:144
uint64 XLogRecPtr
Definition: xlogdefs.h:21
#define Assert(condition)
Definition: c.h:804
OffsetNumber * spl_right
Definition: gist.h:147
static FullTransactionId FullTransactionIdFromEpochAndXid(uint32 epoch, TransactionId xid)
Definition: transam.h:71
#define MAXALIGN(LEN)
Definition: c.h:757
XLogRecPtr GistNSN
Definition: gist.h:62
PageGistNSN nsn
Definition: gist.h:79
static FullTransactionId GistPageGetDeleteXid(Page page)
Definition: gist.h:215
GISTPageOpaqueData * GISTPageOpaque
Definition: gist.h:85
BlockNumber rightlink
Definition: gist.h:80
#define F_DELETED
Definition: gist.h:47
OffsetNumber offset
Definition: gist.h:163
#define offsetof(type, field)
Definition: c.h:727
Pointer Page
Definition: bufpage.h:78