src/backend/catalog/pg_largeobject.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * pg_largeobject.c
   4  *        routines to support manipulation of the pg_largeobject relation
   5  *
   6  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        $PostgreSQL$
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #include "postgres.h"
  16
  17 #include "access/genam.h"
  18 #include "access/heapam.h"
  19 #include "catalog/indexing.h"
  20 #include "catalog/pg_largeobject.h"
  21 #include "utils/builtins.h"
  22 #include "utils/fmgroids.h"
  23 #include "utils/rel.h"
  24 #include "utils/tqual.h"
  25
  26
  27 /*
  28  * Create a large object having the given LO identifier.
  29  *
  30  * We do this by inserting an empty first page, so that the object will
  31  * appear to exist with size 0.  Note that the unique index will reject
  32  * an attempt to create a duplicate page.
  33  */
  34 void
  35 LargeObjectCreate(Oid loid)
  36 {
  37         Relation        pg_largeobject;
  38         HeapTuple       ntup;
  39         Datum           values[Natts_pg_largeobject];
  40         bool            nulls[Natts_pg_largeobject];
  41         int                     i;
  42
  43         pg_largeobject = heap_open(LargeObjectRelationId, RowExclusiveLock);
  44
  45         /*
  46          * Form new tuple
  47          */
  48         for (i = 0; i < Natts_pg_largeobject; i++)
  49         {
  50                 values[i] = (Datum) NULL;
  51                 nulls[i] = false;
  52         }
  53
  54         i = 0;
  55         values[i++] = ObjectIdGetDatum(loid);
  56         values[i++] = Int32GetDatum(0);
  57         values[i++] = DirectFunctionCall1(byteain,
  58                                                                           CStringGetDatum(""));
  59
  60         ntup = heap_form_tuple(pg_largeobject->rd_att, values, nulls);
  61
  62         /*
  63          * Insert it
  64          */
  65         simple_heap_insert(pg_largeobject, ntup);
  66
  67         /* Update indexes */
  68         CatalogUpdateIndexes(pg_largeobject, ntup);
  69
  70         heap_close(pg_largeobject, RowExclusiveLock);
  71
  72         heap_freetuple(ntup);
  73 }
  74
  75 void
  76 LargeObjectDrop(Oid loid)
  77 {
  78         bool            found = false;
  79         Relation        pg_largeobject;
  80         ScanKeyData skey[1];
  81         SysScanDesc sd;
  82         HeapTuple       tuple;
  83
  84         ScanKeyInit(&skey[0],
  85                                 Anum_pg_largeobject_loid,
  86                                 BTEqualStrategyNumber, F_OIDEQ,
  87                                 ObjectIdGetDatum(loid));
  88
  89         pg_largeobject = heap_open(LargeObjectRelationId, RowExclusiveLock);
  90
  91         sd = systable_beginscan(pg_largeobject, LargeObjectLOidPNIndexId, true,
  92                                                         SnapshotNow, 1, skey);
  93
  94         while ((tuple = systable_getnext(sd)) != NULL)
  95         {
  96                 simple_heap_delete(pg_largeobject, &tuple->t_self);
  97                 found = true;
  98         }
  99
 100         systable_endscan(sd);
 101
 102         heap_close(pg_largeobject, RowExclusiveLock);
 103
 104         if (!found)
 105                 ereport(ERROR,
 106                                 (errcode(ERRCODE_UNDEFINED_OBJECT),
 107                                  errmsg("large object %u does not exist", loid)));
 108 }
 109
 110 bool
 111 LargeObjectExists(Oid loid)
 112 {
 113         bool            retval = false;
 114         Relation        pg_largeobject;
 115         ScanKeyData skey[1];
 116         SysScanDesc sd;
 117
 118         /*
 119          * See if we can find any tuples belonging to the specified LO
 120          */
 121         ScanKeyInit(&skey[0],
 122                                 Anum_pg_largeobject_loid,
 123                                 BTEqualStrategyNumber, F_OIDEQ,
 124                                 ObjectIdGetDatum(loid));
 125
 126         pg_largeobject = heap_open(LargeObjectRelationId, AccessShareLock);
 127
 128         sd = systable_beginscan(pg_largeobject, LargeObjectLOidPNIndexId, true,
 129                                                         SnapshotNow, 1, skey);
 130
 131         if (systable_getnext(sd) != NULL)
 132                 retval = true;
 133
 134         systable_endscan(sd);
 135
 136         heap_close(pg_largeobject, AccessShareLock);
 137
 138         return retval;
 139 }