postgresql/src/backend/catalog/pg_largeobject.c

/*-------------------------------------------------------------------------
 *
 * pg_largeobject.c
 *	  routines to support manipulation of the pg_largeobject relation
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/catalog/pg_largeobject.c,v 1.16 2003/08/04 02:39:58 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "catalog/catname.h"
#include "catalog/indexing.h"
#include "catalog/pg_largeobject.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"


/*
 * Create a large object having the given LO identifier.
 *
 * We do this by inserting an empty first page, so that the object will
 * appear to exist with size 0.  Note that the unique index will reject
 * an attempt to create a duplicate page.
 */
void
LargeObjectCreate(Oid loid)
{
	Relation	pg_largeobject;
	HeapTuple	ntup;
	Datum		values[Natts_pg_largeobject];
	char		nulls[Natts_pg_largeobject];
	int			i;

	pg_largeobject = heap_openr(LargeObjectRelationName, RowExclusiveLock);

	/*
	 * Form new tuple
	 */
	for (i = 0; i < Natts_pg_largeobject; i++)
	{
		values[i] = (Datum) NULL;
		nulls[i] = ' ';
	}

	i = 0;
	values[i++] = ObjectIdGetDatum(loid);
	values[i++] = Int32GetDatum(0);
	values[i++] = DirectFunctionCall1(byteain,
									  CStringGetDatum(""));

	ntup = heap_formtuple(pg_largeobject->rd_att, values, nulls);

	/*
	 * Insert it
	 */
	simple_heap_insert(pg_largeobject, ntup);

	/* Update indexes */
	CatalogUpdateIndexes(pg_largeobject, ntup);

	heap_close(pg_largeobject, RowExclusiveLock);

	heap_freetuple(ntup);
}

void
LargeObjectDrop(Oid loid)
{
	bool		found = false;
	Relation	pg_largeobject;
	Relation	pg_lo_idx;
	ScanKeyData skey[1];
	IndexScanDesc sd;
	HeapTuple	tuple;

	ScanKeyEntryInitialize(&skey[0],
						   (bits16) 0x0,
						   (AttrNumber) 1,
						   (RegProcedure) F_OIDEQ,
						   ObjectIdGetDatum(loid));

	pg_largeobject = heap_openr(LargeObjectRelationName, RowShareLock);
	pg_lo_idx = index_openr(LargeObjectLOidPNIndex);

	sd = index_beginscan(pg_largeobject, pg_lo_idx, SnapshotNow, 1, skey);

	while ((tuple = index_getnext(sd, ForwardScanDirection)) != NULL)
	{
		simple_heap_delete(pg_largeobject, &tuple->t_self);
		found = true;
	}

	index_endscan(sd);

	index_close(pg_lo_idx);
	heap_close(pg_largeobject, RowShareLock);

	if (!found)
		ereport(ERROR,
				(errcode(ERRCODE_UNDEFINED_OBJECT),
				 errmsg("large object %u does not exist", loid)));
}

bool
LargeObjectExists(Oid loid)
{
	bool		retval = false;
	Relation	pg_largeobject;
	Relation	pg_lo_idx;
	ScanKeyData skey[1];
	IndexScanDesc sd;
	HeapTuple	tuple;

	/*
	 * See if we can find any tuples belonging to the specified LO
	 */
	ScanKeyEntryInitialize(&skey[0],
						   (bits16) 0x0,
						   (AttrNumber) 1,
						   (RegProcedure) F_OIDEQ,
						   ObjectIdGetDatum(loid));

	pg_largeobject = heap_openr(LargeObjectRelationName, RowShareLock);
	pg_lo_idx = index_openr(LargeObjectLOidPNIndex);

	sd = index_beginscan(pg_largeobject, pg_lo_idx, SnapshotNow, 1, skey);

	if ((tuple = index_getnext(sd, ForwardScanDirection)) != NULL)
		retval = true;

	index_endscan(sd);

	index_close(pg_lo_idx);
	heap_close(pg_largeobject, RowShareLock);

	return retval;
}