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/*-------------------------------------------------------------------------
*
* pg_largeobject.c
* routines to support manipulation of the pg_largeobject relation
*
* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/catalog/pg_largeobject.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/pg_largeobject.h"
#include "catalog/pg_largeobject_metadata.h"
#include "miscadmin.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"
/*
* Create a large object having the given LO identifier.
*
* We create a new large object by inserting an entry into
* pg_largeobject_metadata without any data pages, so that the object
* will appear to exist with size 0.
*/
Oid
LargeObjectCreate(Oid loid)
{
Relation pg_lo_meta;
HeapTuple ntup;
Oid loid_new;
Datum values[Natts_pg_largeobject_metadata];
bool nulls[Natts_pg_largeobject_metadata];
pg_lo_meta = table_open(LargeObjectMetadataRelationId,
RowExclusiveLock);
/*
* Insert metadata of the largeobject
*/
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
if (OidIsValid(loid))
loid_new = loid;
else
loid_new = GetNewOidWithIndex(pg_lo_meta,
LargeObjectMetadataOidIndexId,
Anum_pg_largeobject_metadata_oid);
values[Anum_pg_largeobject_metadata_oid - 1] = ObjectIdGetDatum(loid_new);
values[Anum_pg_largeobject_metadata_lomowner - 1]
= ObjectIdGetDatum(GetUserId());
nulls[Anum_pg_largeobject_metadata_lomacl - 1] = true;
ntup = heap_form_tuple(RelationGetDescr(pg_lo_meta),
values, nulls);
CatalogTupleInsert(pg_lo_meta, ntup);
heap_freetuple(ntup);
table_close(pg_lo_meta, RowExclusiveLock);
return loid_new;
}
/*
* Drop a large object having the given LO identifier. Both the data pages
* and metadata must be dropped.
*/
void
LargeObjectDrop(Oid loid)
{
Relation pg_lo_meta;
Relation pg_largeobject;
ScanKeyData skey[1];
SysScanDesc scan;
HeapTuple tuple;
pg_lo_meta = table_open(LargeObjectMetadataRelationId,
RowExclusiveLock);
pg_largeobject = table_open(LargeObjectRelationId,
RowExclusiveLock);
/*
* Delete an entry from pg_largeobject_metadata
*/
ScanKeyInit(&skey[0],
Anum_pg_largeobject_metadata_oid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(loid));
scan = systable_beginscan(pg_lo_meta,
LargeObjectMetadataOidIndexId, true,
NULL, 1, skey);
tuple = systable_getnext(scan);
if (!HeapTupleIsValid(tuple))
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("large object %u does not exist", loid)));
CatalogTupleDelete(pg_lo_meta, &tuple->t_self);
systable_endscan(scan);
/*
* Delete all the associated entries from pg_largeobject
*/
ScanKeyInit(&skey[0],
Anum_pg_largeobject_loid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(loid));
scan = systable_beginscan(pg_largeobject,
LargeObjectLOidPNIndexId, true,
NULL, 1, skey);
while (HeapTupleIsValid(tuple = systable_getnext(scan)))
{
CatalogTupleDelete(pg_largeobject, &tuple->t_self);
}
systable_endscan(scan);
table_close(pg_largeobject, RowExclusiveLock);
table_close(pg_lo_meta, RowExclusiveLock);
}
/*
* LargeObjectExists
*
* We don't use the system cache for large object metadata, for fear of
* using too much local memory.
*
* This function always scans the system catalog using an up-to-date snapshot,
* so it should not be used when a large object is opened in read-only mode
* (because large objects opened in read only mode are supposed to be viewed
* relative to the caller's snapshot, whereas in read-write mode they are
* relative to a current snapshot).
*/
bool
LargeObjectExists(Oid loid)
{
Relation pg_lo_meta;
ScanKeyData skey[1];
SysScanDesc sd;
HeapTuple tuple;
bool retval = false;
ScanKeyInit(&skey[0],
Anum_pg_largeobject_metadata_oid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(loid));
pg_lo_meta = table_open(LargeObjectMetadataRelationId,
AccessShareLock);
sd = systable_beginscan(pg_lo_meta,
LargeObjectMetadataOidIndexId, true,
NULL, 1, skey);
tuple = systable_getnext(sd);
if (HeapTupleIsValid(tuple))
retval = true;
systable_endscan(sd);
table_close(pg_lo_meta, AccessShareLock);
return retval;
}
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