Line data Source code
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"
24 : #include "catalog/pg_largeobject_metadata.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
40 15 : LargeObjectCreate(Oid loid)
41 : {
42 : Relation pg_lo_meta;
43 : HeapTuple ntup;
44 : Oid loid_new;
45 : Datum values[Natts_pg_largeobject_metadata];
46 : bool nulls[Natts_pg_largeobject_metadata];
47 :
48 15 : pg_lo_meta = heap_open(LargeObjectMetadataRelationId,
49 : RowExclusiveLock);
50 :
51 : /*
52 : * Insert metadata of the largeobject
53 : */
54 15 : memset(values, 0, sizeof(values));
55 15 : memset(nulls, false, sizeof(nulls));
56 :
57 : values[Anum_pg_largeobject_metadata_lomowner - 1]
58 15 : = ObjectIdGetDatum(GetUserId());
59 15 : nulls[Anum_pg_largeobject_metadata_lomacl - 1] = true;
60 :
61 15 : ntup = heap_form_tuple(RelationGetDescr(pg_lo_meta),
62 : values, nulls);
63 15 : if (OidIsValid(loid))
64 8 : HeapTupleSetOid(ntup, loid);
65 :
66 15 : loid_new = CatalogTupleInsert(pg_lo_meta, ntup);
67 15 : Assert(!OidIsValid(loid) || loid == loid_new);
68 :
69 15 : heap_freetuple(ntup);
70 :
71 15 : heap_close(pg_lo_meta, RowExclusiveLock);
72 :
73 15 : 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
81 12 : LargeObjectDrop(Oid loid)
82 : {
83 : Relation pg_lo_meta;
84 : Relation pg_largeobject;
85 : ScanKeyData skey[1];
86 : SysScanDesc scan;
87 : HeapTuple tuple;
88 :
89 12 : pg_lo_meta = heap_open(LargeObjectMetadataRelationId,
90 : RowExclusiveLock);
91 :
92 12 : pg_largeobject = heap_open(LargeObjectRelationId,
93 : RowExclusiveLock);
94 :
95 : /*
96 : * Delete an entry from pg_largeobject_metadata
97 : */
98 12 : ScanKeyInit(&skey[0],
99 : ObjectIdAttributeNumber,
100 : BTEqualStrategyNumber, F_OIDEQ,
101 : ObjectIdGetDatum(loid));
102 :
103 12 : scan = systable_beginscan(pg_lo_meta,
104 : LargeObjectMetadataOidIndexId, true,
105 : NULL, 1, skey);
106 :
107 12 : tuple = systable_getnext(scan);
108 12 : if (!HeapTupleIsValid(tuple))
109 0 : ereport(ERROR,
110 : (errcode(ERRCODE_UNDEFINED_OBJECT),
111 : errmsg("large object %u does not exist", loid)));
112 :
113 12 : CatalogTupleDelete(pg_lo_meta, &tuple->t_self);
114 :
115 12 : systable_endscan(scan);
116 :
117 : /*
118 : * Delete all the associated entries from pg_largeobject
119 : */
120 12 : ScanKeyInit(&skey[0],
121 : Anum_pg_largeobject_loid,
122 : BTEqualStrategyNumber, F_OIDEQ,
123 : ObjectIdGetDatum(loid));
124 :
125 12 : scan = systable_beginscan(pg_largeobject,
126 : LargeObjectLOidPNIndexId, true,
127 : NULL, 1, skey);
128 1344 : while (HeapTupleIsValid(tuple = systable_getnext(scan)))
129 : {
130 1320 : CatalogTupleDelete(pg_largeobject, &tuple->t_self);
131 : }
132 :
133 12 : systable_endscan(scan);
134 :
135 12 : heap_close(pg_largeobject, RowExclusiveLock);
136 :
137 12 : heap_close(pg_lo_meta, RowExclusiveLock);
138 12 : }
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
153 17 : LargeObjectExists(Oid loid)
154 : {
155 : Relation pg_lo_meta;
156 : ScanKeyData skey[1];
157 : SysScanDesc sd;
158 : HeapTuple tuple;
159 17 : bool retval = false;
160 :
161 17 : ScanKeyInit(&skey[0],
162 : ObjectIdAttributeNumber,
163 : BTEqualStrategyNumber, F_OIDEQ,
164 : ObjectIdGetDatum(loid));
165 :
166 17 : pg_lo_meta = heap_open(LargeObjectMetadataRelationId,
167 : AccessShareLock);
168 :
169 17 : sd = systable_beginscan(pg_lo_meta,
170 : LargeObjectMetadataOidIndexId, true,
171 : NULL, 1, skey);
172 :
173 17 : tuple = systable_getnext(sd);
174 17 : if (HeapTupleIsValid(tuple))
175 14 : retval = true;
176 :
177 17 : systable_endscan(sd);
178 :
179 17 : heap_close(pg_lo_meta, AccessShareLock);
180 :
181 17 : return retval;
182 : }
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