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pg_largeobject.c
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1 /*-------------------------------------------------------------------------
2  *
3  * pg_largeobject.c
4  * routines to support manipulation of the pg_largeobject relation
5  *
6  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/catalog/pg_largeobject.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 #include "postgres.h"
16 
17 #include "access/genam.h"
18 #include "access/heapam.h"
19 #include "access/htup_details.h"
20 #include "access/sysattr.h"
21 #include "catalog/dependency.h"
22 #include "catalog/indexing.h"
23 #include "catalog/pg_largeobject.h"
25 #include "miscadmin.h"
26 #include "utils/acl.h"
27 #include "utils/fmgroids.h"
28 #include "utils/rel.h"
29 #include "utils/tqual.h"
30 
31 
32 /*
33  * Create a large object having the given LO identifier.
34  *
35  * We create a new large object by inserting an entry into
36  * pg_largeobject_metadata without any data pages, so that the object
37  * will appear to exist with size 0.
38  */
39 Oid
41 {
42  Relation pg_lo_meta;
43  HeapTuple ntup;
44  Oid loid_new;
47 
50 
51  /*
52  * Insert metadata of the largeobject
53  */
54  memset(values, 0, sizeof(values));
55  memset(nulls, false, sizeof(nulls));
56 
59  nulls[Anum_pg_largeobject_metadata_lomacl - 1] = true;
60 
61  ntup = heap_form_tuple(RelationGetDescr(pg_lo_meta),
62  values, nulls);
63  if (OidIsValid(loid))
64  HeapTupleSetOid(ntup, loid);
65 
66  loid_new = CatalogTupleInsert(pg_lo_meta, ntup);
67  Assert(!OidIsValid(loid) || loid == loid_new);
68 
69  heap_freetuple(ntup);
70 
71  heap_close(pg_lo_meta, RowExclusiveLock);
72 
73  return loid_new;
74 }
75 
76 /*
77  * Drop a large object having the given LO identifier. Both the data pages
78  * and metadata must be dropped.
79  */
80 void
82 {
83  Relation pg_lo_meta;
84  Relation pg_largeobject;
85  ScanKeyData skey[1];
86  SysScanDesc scan;
87  HeapTuple tuple;
88 
91 
92  pg_largeobject = heap_open(LargeObjectRelationId,
94 
95  /*
96  * Delete an entry from pg_largeobject_metadata
97  */
98  ScanKeyInit(&skey[0],
100  BTEqualStrategyNumber, F_OIDEQ,
101  ObjectIdGetDatum(loid));
102 
103  scan = systable_beginscan(pg_lo_meta,
105  NULL, 1, skey);
106 
107  tuple = systable_getnext(scan);
108  if (!HeapTupleIsValid(tuple))
109  ereport(ERROR,
110  (errcode(ERRCODE_UNDEFINED_OBJECT),
111  errmsg("large object %u does not exist", loid)));
112 
113  CatalogTupleDelete(pg_lo_meta, &tuple->t_self);
114 
115  systable_endscan(scan);
116 
117  /*
118  * Delete all the associated entries from pg_largeobject
119  */
120  ScanKeyInit(&skey[0],
122  BTEqualStrategyNumber, F_OIDEQ,
123  ObjectIdGetDatum(loid));
124 
125  scan = systable_beginscan(pg_largeobject,
127  NULL, 1, skey);
128  while (HeapTupleIsValid(tuple = systable_getnext(scan)))
129  {
130  CatalogTupleDelete(pg_largeobject, &tuple->t_self);
131  }
132 
133  systable_endscan(scan);
134 
135  heap_close(pg_largeobject, RowExclusiveLock);
136 
137  heap_close(pg_lo_meta, RowExclusiveLock);
138 }
139 
140 /*
141  * LargeObjectExists
142  *
143  * We don't use the system cache for large object metadata, for fear of
144  * using too much local memory.
145  *
146  * This function always scans the system catalog using an up-to-date snapshot,
147  * so it should not be used when a large object is opened in read-only mode
148  * (because large objects opened in read only mode are supposed to be viewed
149  * relative to the caller's snapshot, whereas in read-write mode they are
150  * relative to a current snapshot).
151  */
152 bool
154 {
155  Relation pg_lo_meta;
156  ScanKeyData skey[1];
157  SysScanDesc sd;
158  HeapTuple tuple;
159  bool retval = false;
160 
161  ScanKeyInit(&skey[0],
163  BTEqualStrategyNumber, F_OIDEQ,
164  ObjectIdGetDatum(loid));
165 
168 
169  sd = systable_beginscan(pg_lo_meta,
171  NULL, 1, skey);
172 
173  tuple = systable_getnext(sd);
174  if (HeapTupleIsValid(tuple))
175  retval = true;
176 
177  systable_endscan(sd);
178 
179  heap_close(pg_lo_meta, AccessShareLock);
180 
181  return retval;
182 }
void systable_endscan(SysScanDesc sysscan)
Definition: genam.c:499
#define RelationGetDescr(relation)
Definition: rel.h:425
Oid GetUserId(void)
Definition: miscinit.c:283
#define ObjectIdAttributeNumber
Definition: sysattr.h:22
#define AccessShareLock
Definition: lockdefs.h:36
int errcode(int sqlerrcode)
Definition: elog.c:575
void CatalogTupleDelete(Relation heapRel, ItemPointer tid)
Definition: indexing.c:255
HeapTuple heap_form_tuple(TupleDesc tupleDescriptor, Datum *values, bool *isnull)
Definition: heaptuple.c:692
#define heap_close(r, l)
Definition: heapam.h:97
Oid LargeObjectCreate(Oid loid)
void heap_freetuple(HeapTuple htup)
Definition: heaptuple.c:1374
unsigned int Oid
Definition: postgres_ext.h:31
#define OidIsValid(objectId)
Definition: c.h:538
SysScanDesc systable_beginscan(Relation heapRelation, Oid indexId, bool indexOK, Snapshot snapshot, int nkeys, ScanKey key)
Definition: genam.c:328
#define Natts_pg_largeobject_metadata
#define HeapTupleSetOid(tuple, oid)
Definition: htup_details.h:698
HeapTuple systable_getnext(SysScanDesc sysscan)
Definition: genam.c:416
#define ObjectIdGetDatum(X)
Definition: postgres.h:513
#define ERROR
Definition: elog.h:43
Oid CatalogTupleInsert(Relation heapRel, HeapTuple tup)
Definition: indexing.c:162
ItemPointerData t_self
Definition: htup.h:65
#define LargeObjectLOidPNIndexId
Definition: indexing.h:180
#define RowExclusiveLock
Definition: lockdefs.h:38
#define ereport(elevel, rest)
Definition: elog.h:122
void LargeObjectDrop(Oid loid)
#define LargeObjectMetadataOidIndexId
Definition: indexing.h:183
uintptr_t Datum
Definition: postgres.h:372
Relation heap_open(Oid relationId, LOCKMODE lockmode)
Definition: heapam.c:1287
#define Anum_pg_largeobject_metadata_lomowner
#define HeapTupleIsValid(tuple)
Definition: htup.h:77
#define NULL
Definition: c.h:229
#define Assert(condition)
Definition: c.h:675
#define LargeObjectMetadataRelationId
static Datum values[MAXATTR]
Definition: bootstrap.c:162
bool LargeObjectExists(Oid loid)
int errmsg(const char *fmt,...)
Definition: elog.c:797
#define Anum_pg_largeobject_metadata_lomacl
void ScanKeyInit(ScanKey entry, AttrNumber attributeNumber, StrategyNumber strategy, RegProcedure procedure, Datum argument)
Definition: scankey.c:76
#define Anum_pg_largeobject_loid
#define LargeObjectRelationId
#define BTEqualStrategyNumber
Definition: stratnum.h:31