postgresql/src/backend/commands/command.c

/*-------------------------------------------------------------------------
 *
 * command.c
 *	  random postgres portal and utility support code
 *
 * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.139 2001/08/10 14:30:14 momjian Exp $
 *
 * NOTES
 *	  The PerformAddAttribute() code, like most of the relation
 *	  manipulating code in the commands/ directory, should go
 *	  someplace closer to the lib/catalog code.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/tuptoaster.h"
#include "catalog/catalog.h"
#include "catalog/catname.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "catalog/indexing.h"
#include "catalog/pg_attrdef.h"
#include "catalog/pg_index.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_type.h"
#include "commands/command.h"
#include "commands/trigger.h"
#include "executor/execdefs.h"
#include "executor/executor.h"
#include "miscadmin.h"
#include "optimizer/clauses.h"
#include "optimizer/planmain.h"
#include "optimizer/prep.h"
#include "parser/parse.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "utils/relcache.h"
#include "utils/temprel.h"


static void drop_default(Oid relid, int16 attnum);
static bool needs_toast_table(Relation rel);
static bool is_relation(char *name);


/* --------------------------------
 *		PortalCleanup
 * --------------------------------
 */
void
PortalCleanup(Portal portal)
{
	MemoryContext oldcontext;

	/*
	 * sanity checks
	 */
	AssertArg(PortalIsValid(portal));
	AssertArg(portal->cleanup == PortalCleanup);

	/*
	 * set proper portal-executor context before calling ExecMain.
	 */
	oldcontext = MemoryContextSwitchTo(PortalGetHeapMemory(portal));

	/*
	 * tell the executor to shutdown the query
	 */
	ExecutorEnd(PortalGetQueryDesc(portal), PortalGetState(portal));

	/*
	 * switch back to previous context
	 */
	MemoryContextSwitchTo(oldcontext);
}

/* --------------------------------
 *		PerformPortalFetch
 * --------------------------------
 */
void
PerformPortalFetch(char *name,
				   bool forward,
				   int count,
				   char *tag,
				   CommandDest dest)
{
	Portal		portal;
	QueryDesc  *queryDesc;
	EState	   *estate;
	MemoryContext oldcontext;
	bool		faked_desc = false;

	/*
	 * sanity checks
	 */
	if (name == NULL)
	{
		elog(NOTICE, "PerformPortalFetch: missing portal name");
		return;
	}

	/*
	 * get the portal from the portal name
	 */
	portal = GetPortalByName(name);
	if (!PortalIsValid(portal))
	{
		elog(NOTICE, "PerformPortalFetch: portal \"%s\" not found",
			 name);
		return;
	}

	/*
	 * switch into the portal context
	 */
	oldcontext = MemoryContextSwitchTo(PortalGetHeapMemory(portal));

	/*
	 * tell the destination to prepare to receive some tuples.
	 *
	 * If we've been asked for a MOVE, make a temporary QueryDesc with the
	 * appropriate dummy destination.
	 */
	queryDesc = PortalGetQueryDesc(portal);
	estate = PortalGetState(portal);

	if (dest != queryDesc->dest)			/* MOVE */
	{
		QueryDesc  *qdesc = (QueryDesc *) palloc(sizeof(QueryDesc));

		memcpy(qdesc, queryDesc, sizeof(QueryDesc));
		qdesc->dest = dest;
		queryDesc = qdesc;
		faked_desc = true;
	}

	BeginCommand(name,
				 queryDesc->operation,
				 PortalGetTupleDesc(portal),
				 false,			/* portal fetches don't end up in
								 * relations */
				 false,			/* this is a portal fetch, not a "retrieve
								 * portal" */
				 tag,
				 dest);

	/*
	 * Determine which direction to go in, and check to see if we're
	 * already at the end of the available tuples in that direction.  If
	 * so, do nothing.	(This check exists because not all plan node types
	 * are robust about being called again if they've already returned
	 * NULL once.)	If it's OK to do the fetch, call the executor.  Then,
	 * update the atStart/atEnd state depending on the number of tuples
	 * that were retrieved.
	 */
	if (forward)
	{
		if (!portal->atEnd)
		{
			ExecutorRun(queryDesc, estate, EXEC_FOR, (long) count);
			/*
			 *	I use CMD_UPDATE, because no CMD_MOVE or the like
			 *	exists, and I would like to provide the same
			 *	kind of info as CMD_UPDATE
			 */
			UpdateCommandInfo(CMD_UPDATE, 0, estate->es_processed);
			if (estate->es_processed > 0)
				portal->atStart = false;		/* OK to back up now */
			if (count <= 0 || (int) estate->es_processed < count)
				portal->atEnd = true;	/* we retrieved 'em all */
		}
	}
	else
	{
		if (!portal->atStart)
		{
			ExecutorRun(queryDesc, estate, EXEC_BACK, (long) count);
			/*
			 *	I use CMD_UPDATE, because no CMD_MOVE or the like
			 *	exists, and I would like to provide the same
			 *	kind of info as CMD_UPDATE
			 */
			UpdateCommandInfo(CMD_UPDATE, 0, estate->es_processed);
			if (estate->es_processed > 0)
				portal->atEnd = false;	/* OK to go forward now */
			if (count <= 0 || (int) estate->es_processed < count)
				portal->atStart = true; /* we retrieved 'em all */
		}
	}

	/*
	 * Clean up and switch back to old context.
	 */
	if (faked_desc)			/* MOVE */
		pfree(queryDesc);

	MemoryContextSwitchTo(oldcontext);

	/*
	 * Note: the "end-of-command" tag is returned by higher-level utility
	 * code
	 */
}

/* --------------------------------
 *		PerformPortalClose
 * --------------------------------
 */
void
PerformPortalClose(char *name, CommandDest dest)
{
	Portal		portal;

	/*
	 * sanity checks
	 */
	if (name == NULL)
	{
		elog(NOTICE, "PerformPortalClose: missing portal name");
		return;
	}

	/*
	 * get the portal from the portal name
	 */
	portal = GetPortalByName(name);
	if (!PortalIsValid(portal))
	{
		elog(NOTICE, "PerformPortalClose: portal \"%s\" not found",
			 name);
		return;
	}

	/*
	 * Note: PortalCleanup is called as a side-effect
	 */
	PortalDrop(&portal);
}

/* ----------------
 *		AlterTableAddColumn
 *		(formerly known as PerformAddAttribute)
 *
 *		adds an additional attribute to a relation
 *
 *		Adds attribute field(s) to a relation.	Each new attribute
 *		is given attnums in sequential order and is added to the
 *		ATTRIBUTE relation.  If the AMI fails, defunct tuples will
 *		remain in the ATTRIBUTE relation for later vacuuming.
 *		Later, there may be some reserved attribute names???
 *
 *		(If needed, can instead use elog to handle exceptions.)
 *
 *		Note:
 *				Initial idea of ordering the tuple attributes so that all
 *		the variable length domains occured last was scratched.  Doing
 *		so would not speed access too much (in general) and would create
 *		many complications in formtuple, heap_getattr, and addattribute.
 *
 *		scan attribute catalog for name conflict (within rel)
 *		scan type catalog for absence of data type (if not arg)
 *		create attnum magically???
 *		create attribute tuple
 *		insert attribute in attribute catalog
 *		modify reldesc
 *		create new relation tuple
 *		insert new relation in relation catalog
 *		delete original relation from relation catalog
 * ----------------
 */
void
AlterTableAddColumn(const char *relationName,
					bool inherits,
					ColumnDef *colDef)
{
	Relation	rel,
				attrdesc;
	Oid			myrelid;
	HeapTuple	reltup;
	HeapTuple	newreltup;
	HeapTuple	attributeTuple;
	Form_pg_attribute attribute;
	FormData_pg_attribute attributeD;
	int			i;
	int			minattnum,
				maxatts;
	Relation	idescs[Num_pg_attr_indices];
	Relation	ridescs[Num_pg_class_indices];
	bool		hasindex;

	/*
	 * permissions checking.  this would normally be done in utility.c,
	 * but this particular routine is recursive.
	 *
	 * normally, only the owner of a class can change its schema.
	 */
	if (!allowSystemTableMods && IsSystemRelationName(relationName))
		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
			 relationName);
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");

	/*
	 * Grab an exclusive lock on the target table, which we will NOT
	 * release until end of transaction.
	 */
	rel = heap_openr(relationName, AccessExclusiveLock);

	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
			 relationName);

	myrelid = RelationGetRelid(rel);
	heap_close(rel, NoLock);	/* close rel but keep lock! */

	/*
	 * we can't add a not null attribute
	 */
	if (colDef->is_not_null)
		elog(ERROR, "Can't add a NOT NULL attribute to an existing relation");

	if (colDef->raw_default || colDef->cooked_default)
		elog(ERROR, "Adding columns with defaults is not implemented.");


	/*
	 * if the first element in the 'schema' list is a "*" then we are
	 * supposed to add this attribute to all classes that inherit from
	 * 'relationName' (as well as to 'relationName').
	 *
	 * any permissions or problems with duplicate attributes will cause the
	 * whole transaction to abort, which is what we want -- all or
	 * nothing.
	 */
	if (colDef != NULL)
	{
		if (inherits)
		{
			List	   *child,
					   *children;

			/* this routine is actually in the planner */
			children = find_all_inheritors(myrelid);

			/*
			 * find_all_inheritors does the recursive search of the
			 * inheritance hierarchy, so all we have to do is process all
			 * of the relids in the list that it returns.
			 */
			foreach(child, children)
			{
				Oid			childrelid = lfirsti(child);
				char	   *childrelname;

				if (childrelid == myrelid)
					continue;
				rel = heap_open(childrelid, AccessExclusiveLock);
				childrelname = pstrdup(RelationGetRelationName(rel));
				heap_close(rel, AccessExclusiveLock);

				AlterTableAddColumn(childrelname, false, colDef);

				pfree(childrelname);
			}
		}
	}

	rel = heap_openr(RelationRelationName, RowExclusiveLock);

	reltup = SearchSysCache(RELNAME,
							PointerGetDatum(relationName),
							0, 0, 0);

	if (!HeapTupleIsValid(reltup))
		elog(ERROR, "ALTER TABLE: relation \"%s\" not found",
			 relationName);

	minattnum = ((Form_pg_class) GETSTRUCT(reltup))->relnatts;
	maxatts = minattnum + 1;
	if (maxatts > MaxHeapAttributeNumber)
		elog(ERROR, "ALTER TABLE: relations limited to %d columns",
			 MaxHeapAttributeNumber);

	attrdesc = heap_openr(AttributeRelationName, RowExclusiveLock);

	/*
	 * Open all (if any) pg_attribute indices
	 */
	hasindex = RelationGetForm(attrdesc)->relhasindex;
	if (hasindex)
		CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, idescs);

	attributeD.attrelid = reltup->t_data->t_oid;

	attributeTuple = heap_addheader(Natts_pg_attribute,
									ATTRIBUTE_TUPLE_SIZE,
									(void *) &attributeD);

	attribute = (Form_pg_attribute) GETSTRUCT(attributeTuple);

	i = 1 + minattnum;

	{
		HeapTuple	typeTuple;
		Form_pg_type tform;
		char	   *typename;
		int			attndims;

		if (SearchSysCacheExists(ATTNAME,
								 ObjectIdGetDatum(reltup->t_data->t_oid),
								 PointerGetDatum(colDef->colname),
								 0, 0))
			elog(ERROR, "ALTER TABLE: column name \"%s\" already exists in table \"%s\"",
				 colDef->colname, relationName);

		/*
		 * check to see if it is an array attribute.
		 */

		typename = colDef->typename->name;

		if (colDef->typename->arrayBounds)
		{
			attndims = length(colDef->typename->arrayBounds);
			typename = makeArrayTypeName(colDef->typename->name);
		}
		else
			attndims = 0;

		typeTuple = SearchSysCache(TYPENAME,
								   PointerGetDatum(typename),
								   0, 0, 0);
		if (!HeapTupleIsValid(typeTuple))
			elog(ERROR, "ALTER TABLE: type \"%s\" does not exist", typename);
		tform = (Form_pg_type) GETSTRUCT(typeTuple);

		namestrcpy(&(attribute->attname), colDef->colname);
		attribute->atttypid = typeTuple->t_data->t_oid;
		attribute->attlen = tform->typlen;
		attribute->attstattarget = DEFAULT_ATTSTATTARGET;
		attribute->attcacheoff = -1;
		attribute->atttypmod = colDef->typename->typmod;
		attribute->attnum = i;
		attribute->attbyval = tform->typbyval;
		attribute->attndims = attndims;
		attribute->attisset = (bool) (tform->typtype == 'c');
		attribute->attstorage = tform->typstorage;
		attribute->attalign = tform->typalign;
		attribute->attnotnull = false;
		attribute->atthasdef = (colDef->raw_default != NULL ||
								colDef->cooked_default != NULL);

		ReleaseSysCache(typeTuple);

		heap_insert(attrdesc, attributeTuple);
		if (hasindex)
			CatalogIndexInsert(idescs,
							   Num_pg_attr_indices,
							   attrdesc,
							   attributeTuple);
	}

	if (hasindex)
		CatalogCloseIndices(Num_pg_attr_indices, idescs);

	heap_close(attrdesc, NoLock);

	/*
	 * Update number of attributes in pg_class tuple
	 */
	newreltup = heap_copytuple(reltup);

	((Form_pg_class) GETSTRUCT(newreltup))->relnatts = maxatts;
	simple_heap_update(rel, &newreltup->t_self, newreltup);

	/* keep catalog indices current */
	CatalogOpenIndices(Num_pg_class_indices, Name_pg_class_indices, ridescs);
	CatalogIndexInsert(ridescs, Num_pg_class_indices, rel, newreltup);
	CatalogCloseIndices(Num_pg_class_indices, ridescs);

	heap_freetuple(newreltup);
	ReleaseSysCache(reltup);

	heap_close(rel, NoLock);

	/*
	 * Automatically create the secondary relation for TOAST if it
	 * formerly had no such but now has toastable attributes.
	 */
	CommandCounterIncrement();
	AlterTableCreateToastTable(relationName, true);
}


/*
 * ALTER TABLE ALTER COLUMN SET/DROP DEFAULT
 */
void
AlterTableAlterColumnDefault(const char *relationName,
							 bool inh, const char *colName,
							 Node *newDefault)
{
	Relation	rel;
	HeapTuple	tuple;
	int16		attnum;
	Oid			myrelid;

	if (!allowSystemTableMods && IsSystemRelationName(relationName))
		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
			 relationName);
#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	rel = heap_openr(relationName, AccessExclusiveLock);
	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
			 relationName);
	myrelid = RelationGetRelid(rel);
	heap_close(rel, NoLock);

	/*
	 * Propagate to children if desired
	 */
	if (inh)
	{
		List	   *child,
				   *children;

		/* this routine is actually in the planner */
		children = find_all_inheritors(myrelid);

		/*
		 * find_all_inheritors does the recursive search of the
		 * inheritance hierarchy, so all we have to do is process all of
		 * the relids in the list that it returns.
		 */
		foreach(child, children)
		{
			Oid			childrelid = lfirsti(child);

			if (childrelid == myrelid)
				continue;
			rel = heap_open(childrelid, AccessExclusiveLock);
			AlterTableAlterColumnDefault(RelationGetRelationName(rel),
										 false, colName, newDefault);
			heap_close(rel, AccessExclusiveLock);
		}
	}

	/* -= now do the thing on this relation =- */

	/* reopen the business */
	rel = heap_openr(relationName, AccessExclusiveLock);

	/*
	 * get the number of the attribute
	 */
	tuple = SearchSysCache(ATTNAME,
						   ObjectIdGetDatum(myrelid),
						   PointerGetDatum(colName),
						   0, 0);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
			 relationName, colName);

	attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;
	ReleaseSysCache(tuple);

	if (newDefault)
	{
		/* SET DEFAULT */
		List	   *rawDefaults = NIL;
		RawColumnDefault *rawEnt;

		/* Get rid of the old one first */
		drop_default(myrelid, attnum);

		rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
		rawEnt->attnum = attnum;
		rawEnt->raw_default = newDefault;
		rawDefaults = lappend(rawDefaults, rawEnt);

		/*
		 * This function is intended for CREATE TABLE, so it processes a
		 * _list_ of defaults, but we just do one.
		 */
		AddRelationRawConstraints(rel, rawDefaults, NIL);
	}
	else
	{
		/* DROP DEFAULT */
		Relation	attr_rel;
		ScanKeyData scankeys[3];
		HeapScanDesc scan;

		attr_rel = heap_openr(AttributeRelationName, RowExclusiveLock);
		ScanKeyEntryInitialize(&scankeys[0], 0x0,
							   Anum_pg_attribute_attrelid, F_OIDEQ,
							   ObjectIdGetDatum(myrelid));
		ScanKeyEntryInitialize(&scankeys[1], 0x0,
							   Anum_pg_attribute_attnum, F_INT2EQ,
							   Int16GetDatum(attnum));
		ScanKeyEntryInitialize(&scankeys[2], 0x0,
							   Anum_pg_attribute_atthasdef, F_BOOLEQ,
							   BoolGetDatum(true));

		scan = heap_beginscan(attr_rel, false, SnapshotNow, 3, scankeys);
		AssertState(scan != NULL);

		if (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
		{
			HeapTuple	newtuple;
			Relation	irelations[Num_pg_attr_indices];

			/* update to false */
			newtuple = heap_copytuple(tuple);
			((Form_pg_attribute) GETSTRUCT(newtuple))->atthasdef = FALSE;
			simple_heap_update(attr_rel, &tuple->t_self, newtuple);

			/* keep the system catalog indices current */
			CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, irelations);
			CatalogIndexInsert(irelations, Num_pg_attr_indices, attr_rel, newtuple);
			CatalogCloseIndices(Num_pg_attr_indices, irelations);

			/* get rid of actual default definition */
			drop_default(myrelid, attnum);
		}

		heap_endscan(scan);
		heap_close(attr_rel, NoLock);
	}

	heap_close(rel, NoLock);
}


static void
drop_default(Oid relid, int16 attnum)
{
	ScanKeyData scankeys[2];
	HeapScanDesc scan;
	Relation	attrdef_rel;
	HeapTuple	tuple;

	attrdef_rel = heap_openr(AttrDefaultRelationName, RowExclusiveLock);
	ScanKeyEntryInitialize(&scankeys[0], 0x0,
						   Anum_pg_attrdef_adrelid, F_OIDEQ,
						   ObjectIdGetDatum(relid));
	ScanKeyEntryInitialize(&scankeys[1], 0x0,
						   Anum_pg_attrdef_adnum, F_INT2EQ,
						   Int16GetDatum(attnum));

	scan = heap_beginscan(attrdef_rel, false, SnapshotNow, 2, scankeys);

	if (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
		simple_heap_delete(attrdef_rel, &tuple->t_self);

	heap_endscan(scan);

	heap_close(attrdef_rel, NoLock);
}


/*
 * ALTER TABLE ALTER COLUMN SET STATISTICS
 */
void
AlterTableAlterColumnStatistics(const char *relationName,
								bool inh, const char *colName,
								Node *statsTarget)
{
	Relation	rel;
	Oid			myrelid;
	int			newtarget;
	Relation	attrelation;
	HeapTuple	tuple;

#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	rel = heap_openr(relationName, AccessExclusiveLock);
	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
			 relationName);
	myrelid = RelationGetRelid(rel);
	heap_close(rel, NoLock);	/* close rel, but keep lock! */

	/*
	 * Propagate to children if desired
	 */
	if (inh)
	{
		List	   *child,
				   *children;

		/* this routine is actually in the planner */
		children = find_all_inheritors(myrelid);

		/*
		 * find_all_inheritors does the recursive search of the
		 * inheritance hierarchy, so all we have to do is process all of
		 * the relids in the list that it returns.
		 */
		foreach(child, children)
		{
			Oid			childrelid = lfirsti(child);

			if (childrelid == myrelid)
				continue;
			rel = heap_open(childrelid, AccessExclusiveLock);
			AlterTableAlterColumnStatistics(RelationGetRelationName(rel),
											false, colName, statsTarget);
			heap_close(rel, AccessExclusiveLock);
		}
	}

	/* -= now do the thing on this relation =- */

	Assert(IsA(statsTarget, Integer));
	newtarget = intVal(statsTarget);

	/* Limit target to sane range (should we raise an error instead?) */
	if (newtarget < 0)
		newtarget = 0;
	else if (newtarget > 1000)
		newtarget = 1000;

	attrelation = heap_openr(AttributeRelationName, RowExclusiveLock);

	tuple = SearchSysCacheCopy(ATTNAME,
							   ObjectIdGetDatum(myrelid),
							   PointerGetDatum(colName),
							   0, 0);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "ALTER TABLE: relation \"%s\" has no column \"%s\"",
			 relationName, colName);

	if (((Form_pg_attribute) GETSTRUCT(tuple))->attnum < 0)
		elog(ERROR, "ALTER TABLE: cannot change system attribute \"%s\"",
			 colName);

	((Form_pg_attribute) GETSTRUCT(tuple))->attstattarget = newtarget;

	simple_heap_update(attrelation, &tuple->t_self, tuple);

	/* keep system catalog indices current */
	{
		Relation	irelations[Num_pg_attr_indices];

		CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, irelations);
		CatalogIndexInsert(irelations, Num_pg_attr_indices, attrelation, tuple);
		CatalogCloseIndices(Num_pg_attr_indices, irelations);
	}

	heap_freetuple(tuple);
	heap_close(attrelation, NoLock);
}


#ifdef	_DROP_COLUMN_HACK__
/*
 *	ALTER TABLE DROP COLUMN trial implementation
 *
 */

/*
 *	system table scan(index scan/sequential scan)
 */
typedef struct SysScanDescData
{
	Relation	heap_rel;
	Relation	irel;
	HeapScanDesc scan;
	IndexScanDesc iscan;
	HeapTupleData tuple;
	Buffer		buffer;
}			SysScanDescData, *SysScanDesc;

static void *
systable_beginscan(Relation rel, const char *indexRelname, int nkeys, ScanKey entry)
{
	bool		hasindex = (rel->rd_rel->relhasindex && !IsIgnoringSystemIndexes());
	SysScanDesc sysscan;

	sysscan = (SysScanDesc) palloc(sizeof(SysScanDescData));
	sysscan->heap_rel = rel;
	sysscan->irel = (Relation) NULL;
	sysscan->tuple.t_datamcxt = NULL;
	sysscan->tuple.t_data = NULL;
	sysscan->buffer = InvalidBuffer;
	if (hasindex)
	{
		sysscan->irel = index_openr((char *) indexRelname);
		sysscan->iscan = index_beginscan(sysscan->irel, false, nkeys, entry);
	}
	else
		sysscan->scan = heap_beginscan(rel, false, SnapshotNow, nkeys, entry);
	return (void *) sysscan;
}

static void
systable_endscan(void *scan)
{
	SysScanDesc sysscan = (SysScanDesc) scan;

	if (sysscan->irel)
	{
		if (BufferIsValid(sysscan->buffer))
			ReleaseBuffer(sysscan->buffer);
		index_endscan(sysscan->iscan);
		index_close(sysscan->irel);
	}
	else
		heap_endscan(sysscan->scan);
	pfree(scan);
}

static HeapTuple
systable_getnext(void *scan)
{
	SysScanDesc sysscan = (SysScanDesc) scan;
	HeapTuple	htup = (HeapTuple) NULL;
	RetrieveIndexResult indexRes;

	if (sysscan->irel)
	{
		if (BufferIsValid(sysscan->buffer))
		{
			ReleaseBuffer(sysscan->buffer);
			sysscan->buffer = InvalidBuffer;
		}
		while (indexRes = index_getnext(sysscan->iscan, ForwardScanDirection), indexRes != NULL)
		{
			sysscan->tuple.t_self = indexRes->heap_iptr;
			heap_fetch(sysscan->heap_rel, SnapshotNow, &sysscan->tuple, &(sysscan->buffer));
			pfree(indexRes);
			if (sysscan->tuple.t_data != NULL)
			{
				htup = &sysscan->tuple;
				break;
			}
		}
	}
	else
		htup = heap_getnext(sysscan->scan, 0);
	return htup;
}

/*
 *	find a specified attribute in a node entry
 */
static bool
find_attribute_walker(Node *node, int *attnump)
{
	if (node == NULL)
		return false;
	if (IsA(node, Var))
	{
		Var		   *var = (Var *) node;

		if (var->varlevelsup == 0 && var->varno == 1 &&
			var->varattno == *attnump)
			return true;
	}
	return expression_tree_walker(node, find_attribute_walker,
								  (void *) attnump);
}

static bool
find_attribute_in_node(Node *node, int attnum)
{
	return find_attribute_walker(node, &attnum);
}

/*
 *	Remove/check references for the column
 */
static bool
RemoveColumnReferences(Oid reloid, int attnum, bool checkonly, HeapTuple reltup)
{
	Relation	indexRelation,
				rcrel;
	ScanKeyData entry;
	HeapScanDesc scan;
	void	   *sysscan;
	HeapTuple	htup,
				indexTuple;
	Form_pg_index index;
	Form_pg_class pgcform = (Form_pg_class) NULL;
	int			i;
	bool		checkok = true;


	if (!checkonly)
		pgcform = (Form_pg_class) GETSTRUCT(reltup);

	/*
	 * Remove/check constraints here
	 */
	ScanKeyEntryInitialize(&entry, (bits16) 0x0, Anum_pg_relcheck_rcrelid,
					   (RegProcedure) F_OIDEQ, ObjectIdGetDatum(reloid));
	rcrel = heap_openr(RelCheckRelationName, RowExclusiveLock);
	sysscan = systable_beginscan(rcrel, RelCheckIndex, 1, &entry);

	while (HeapTupleIsValid(htup = systable_getnext(sysscan)))
	{
		Form_pg_relcheck relcheck;
		char	   *ccbin;
		Node	   *node;

		relcheck = (Form_pg_relcheck) GETSTRUCT(htup);
		ccbin = DatumGetCString(DirectFunctionCall1(textout,
									 PointerGetDatum(&relcheck->rcbin)));
		node = stringToNode(ccbin);
		pfree(ccbin);
		if (find_attribute_in_node(node, attnum))
		{
			if (checkonly)
			{
				checkok = false;
				elog(ERROR, "target column is used in a constraint");
			}
			else
			{
				simple_heap_delete(rcrel, &htup->t_self);
				pgcform->relchecks--;
			}
		}
	}
	systable_endscan(sysscan);
	heap_close(rcrel, NoLock);

	/*
	 * What to do with triggers/rules/views/procedues ?
	 */

	/*
	 * Remove/check indexes
	 */
	indexRelation = heap_openr(IndexRelationName, RowExclusiveLock);
	ScanKeyEntryInitialize(&entry, 0, Anum_pg_index_indrelid, F_OIDEQ,
						   ObjectIdGetDatum(reloid));
	scan = heap_beginscan(indexRelation, false, SnapshotNow, 1, &entry);
	while (HeapTupleIsValid(indexTuple = heap_getnext(scan, 0)))
	{
		index = (Form_pg_index) GETSTRUCT(indexTuple);
		for (i = 0; i < INDEX_MAX_KEYS; i++)
		{
			if (index->indkey[i] == InvalidAttrNumber)
				break;
			else if (index->indkey[i] == attnum)
			{
				if (checkonly)
				{
					checkok = false;
					elog(ERROR, "target column is used in an index");
				}
				else
				{
					htup = SearchSysCache(RELOID,
									 ObjectIdGetDatum(index->indexrelid),
										  0, 0, 0);
					RemoveIndex(NameStr(((Form_pg_class) GETSTRUCT(htup))->relname));
					ReleaseSysCache(htup);
				}
				break;
			}
		}
	}
	heap_endscan(scan);
	heap_close(indexRelation, NoLock);

	return checkok;
}

#endif	 /* _DROP_COLUMN_HACK__ */

/*
 * ALTER TABLE DROP COLUMN
 */
void
AlterTableDropColumn(const char *relationName,
					 bool inh, const char *colName,
					 int behavior)
{
#ifdef	_DROP_COLUMN_HACK__
	Relation	rel,
				attrdesc;
	Oid			myrelid,
				attoid;
	HeapTuple	reltup;
	HeapTupleData classtuple;
	Buffer		buffer;
	Form_pg_attribute attribute;
	HeapTuple	tup;
	Relation	idescs[Num_pg_attr_indices];
	int			attnum;
	bool		hasindex;
	char		dropColname[32];

	if (inh)
		elog(ERROR, "ALTER TABLE / DROP COLUMN with inherit option is not supported yet");

	/*
	 * permissions checking.  this would normally be done in utility.c,
	 * but this particular routine is recursive.
	 *
	 * normally, only the owner of a class can change its schema.
	 */
	if (!allowSystemTableMods && IsSystemRelationName(relationName))
		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
			 relationName);
#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	/*
	 * Grab an exclusive lock on the target table, which we will NOT
	 * release until end of transaction.
	 */
	rel = heap_openr(relationName, AccessExclusiveLock);

	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
			 relationName);

	myrelid = RelationGetRelid(rel);
	heap_close(rel, NoLock);	/* close rel but keep lock! */

	/*
	 * What to do when rel has inheritors ?
	 */
	if (length(find_all_inheritors(myrelid)) > 1)
		elog(ERROR, "ALTER TABLE: cannot drop a column on table that is inherited from");

	/*
	 * lock the pg_class tuple for update
	 */
	rel = heap_openr(RelationRelationName, RowExclusiveLock);
	reltup = SearchSysCache(RELNAME,
							PointerGetDatum(relationName),
							0, 0, 0);
	if (!HeapTupleIsValid(reltup))
		elog(ERROR, "ALTER TABLE: relation \"%s\" not found",
			 relationName);
	classtuple.t_self = reltup->t_self;
	ReleaseSysCache(reltup);

	switch (heap_mark4update(rel, &classtuple, &buffer))
	{
		case HeapTupleSelfUpdated:
		case HeapTupleMayBeUpdated:
			break;
		default:
			elog(ERROR, "couldn't lock pg_class tuple");
	}
	reltup = heap_copytuple(&classtuple);
	ReleaseBuffer(buffer);

	attrdesc = heap_openr(AttributeRelationName, RowExclusiveLock);

	/*
	 * Get the target pg_attribute tuple and make a modifiable copy
	 */
	tup = SearchSysCacheCopy(ATTNAME,
							 ObjectIdGetDatum(reltup->t_data->t_oid),
							 PointerGetDatum(colName),
							 0, 0);
	if (!HeapTupleIsValid(tup))
		elog(ERROR, "ALTER TABLE: column name \"%s\" doesn't exist in table \"%s\"",
			 colName, relationName);

	attribute = (Form_pg_attribute) GETSTRUCT(tup);
	attnum = attribute->attnum;
	if (attnum <= 0)
		elog(ERROR, "ALTER TABLE: column name \"%s\" was already dropped",
			 colName);
	attoid = tup->t_data->t_oid;

	/*
	 * Check constraints/indices etc here
	 */
	if (behavior != CASCADE)
	{
		if (!RemoveColumnReferences(myrelid, attnum, true, NULL))
			elog(ERROR, "the column is referenced");
	}

	/*
	 * change the target pg_attribute tuple
	 */
	sprintf(dropColname, "*already Dropped*%d", attnum);
	namestrcpy(&(attribute->attname), dropColname);
	ATTRIBUTE_DROP_COLUMN(attribute);

	simple_heap_update(attrdesc, &tup->t_self, tup);
	hasindex = (!IsIgnoringSystemIndexes() && RelationGetForm(attrdesc)->relhasindex);
	if (hasindex)
	{
		CatalogOpenIndices(Num_pg_attr_indices, Name_pg_attr_indices, idescs);
		CatalogIndexInsert(idescs, Num_pg_attr_indices,
						   attrdesc, tup);
		CatalogCloseIndices(Num_pg_attr_indices, idescs);
	}
	heap_close(attrdesc, NoLock);
	heap_freetuple(tup);

	/* delete comments */
	DeleteComments(attoid);

	/* delete attrdef */
	drop_default(myrelid, attnum);

	/*
	 * Remove objects which reference this column
	 */
	if (behavior == CASCADE)
	{
		Relation	ridescs[Num_pg_class_indices];

		RemoveColumnReferences(myrelid, attnum, false, reltup);
		/* update pg_class tuple */
		simple_heap_update(rel, &reltup->t_self, reltup);
		CatalogOpenIndices(Num_pg_class_indices, Name_pg_class_indices, ridescs);
		CatalogIndexInsert(ridescs, Num_pg_class_indices, rel, reltup);
		CatalogCloseIndices(Num_pg_class_indices, ridescs);
	}

	heap_freetuple(reltup);
	heap_close(rel, NoLock);
#else
				elog(ERROR, "ALTER TABLE / DROP COLUMN is not implemented");
#endif	 /* _DROP_COLUMN_HACK__ */
}



/*
 * ALTER TABLE ADD CONSTRAINT
 */
void
AlterTableAddConstraint(char *relationName,
						bool inh, Node *newConstraint)
{
	if (newConstraint == NULL)
		elog(ERROR, "ALTER TABLE / ADD CONSTRAINT passed invalid constraint.");

#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	/* Disallow ADD CONSTRAINT on views, indexes, sequences, etc */
	if (!is_relation(relationName))
		elog(ERROR, "ALTER TABLE ADD CONSTRAINT: %s is not a table",
			 relationName);

	switch (nodeTag(newConstraint))
	{
		case T_Constraint:
			{
				Constraint *constr = (Constraint *) newConstraint;

				switch (constr->contype)
				{
					case CONSTR_CHECK:
						{
							ParseState *pstate;
							bool		successful = true;
							HeapScanDesc scan;
							ExprContext *econtext;
							TupleTableSlot *slot;
							HeapTuple	tuple;
							RangeTblEntry *rte;
							List	   *qual;
							List	   *constlist;
							Relation	rel;
							Node	   *expr;
							char	   *name;
							Oid	myrelid;

							if (constr->name)
								name = constr->name;
							else
								name = "<unnamed>";

							constlist = makeList1(constr);

							rel = heap_openr(relationName, AccessExclusiveLock);
							myrelid = RelationGetRelid(rel);

							/* make sure it is not a view */
							if (rel->rd_rel->relkind == RELKIND_VIEW)
								elog(ERROR, "ALTER TABLE: cannot add constraint to a view");

							/*
							 * Scan all of the rows, looking for a false
							 * match
							 */
							scan = heap_beginscan(rel, false, SnapshotNow, 0, NULL);
							AssertState(scan != NULL);

							/*
							 * We need to make a parse state and range
							 * table to allow us to transformExpr and
							 * fix_opids to get a version of the
							 * expression we can pass to ExecQual
							 */
							pstate = make_parsestate(NULL);
							rte = addRangeTableEntry(pstate, relationName, NULL,
													 false, true);
							addRTEtoQuery(pstate, rte, true, true);

							/* Convert the A_EXPR in raw_expr into an EXPR */
							expr = transformExpr(pstate, constr->raw_expr,
												 EXPR_COLUMN_FIRST);

							/*
							 * Make sure it yields a boolean result.
							 */
							if (exprType(expr) != BOOLOID)
								elog(ERROR, "CHECK '%s' does not yield boolean result",
									 name);

							/*
							 * Make sure no outside relations are referred
							 * to.
							 */
							if (length(pstate->p_rtable) != 1)
								elog(ERROR, "Only relation '%s' can be referenced in CHECK",
									 relationName);

							/*
							 * Might as well try to reduce any constant
							 * expressions.
							 */
							expr = eval_const_expressions(expr);

							/* And fix the opids */
							fix_opids(expr);

							qual = makeList1(expr);

							/* Make tuple slot to hold tuples */
							slot = MakeTupleTableSlot();
							ExecSetSlotDescriptor(slot, RelationGetDescr(rel), false);
							/* Make an expression context for ExecQual */
							econtext = MakeExprContext(slot, CurrentMemoryContext);

							/*
							 * Scan through the rows now, checking the
							 * expression at each row.
							 */
							while (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
							{
								ExecStoreTuple(tuple, slot, InvalidBuffer, false);
								if (!ExecQual(qual, econtext, true))
								{
									successful = false;
									break;
								}
								ResetExprContext(econtext);
							}

							FreeExprContext(econtext);
							pfree(slot);

							heap_endscan(scan);

							if (!successful)
								elog(ERROR, "AlterTableAddConstraint: rejected due to CHECK constraint %s", name);

							/*
							 * Call AddRelationRawConstraints to do the
							 * real adding -- It duplicates some of the
							 * above, but does not check the validity of
							 * the constraint against tuples already in
							 * the table.
							 */
							AddRelationRawConstraints(rel, NIL, constlist);
							heap_close(rel, NoLock);

							if (inh) {
								List	   *child,
									   *children;

								/* this routine is actually in the planner */
								children = find_all_inheritors(myrelid);

								/*
								 * find_all_inheritors does the recursive search of the
								 * inheritance hierarchy, so all we have to do is process all
								 * of the relids in the list that it returns.
								 */
								foreach(child, children)
								{
									Oid			childrelid = lfirsti(child);
									char	   *childrelname;
	
									if (childrelid == myrelid)
										continue;
									rel = heap_open(childrelid, AccessExclusiveLock);
									childrelname = pstrdup(RelationGetRelationName(rel));
									heap_close(rel, AccessExclusiveLock);

									AlterTableAddConstraint(childrelname, false, newConstraint);
	
									pfree(childrelname);
								}
							}
							pfree(constlist);

							break;
						}
					case CONSTR_PRIMARY:
						{

							break;
						}
					default:
						elog(ERROR, "ALTER TABLE / ADD CONSTRAINT is not implemented for that constraint type.");
				}
				break;
			}
		case T_FkConstraint:
			{
				FkConstraint *fkconstraint = (FkConstraint *) newConstraint;
				Relation	rel,
							pkrel;
				HeapScanDesc scan;
				HeapTuple	tuple;
				Trigger		trig;
				List	   *list;
				int			count;
				List	   *indexoidlist,
						   *indexoidscan;
				Form_pg_attribute *rel_attrs = NULL;
				int			i;
				bool		found = false;

				Oid     fktypoid[INDEX_MAX_KEYS];
				Oid     pktypoid[INDEX_MAX_KEYS];
				int     attloc;
 
				for (i=0; i<INDEX_MAX_KEYS; i++) 
					fktypoid[i]=pktypoid[i]=0;

				if (is_temp_rel_name(fkconstraint->pktable_name) &&
					!is_temp_rel_name(relationName))
					elog(ERROR, "ALTER TABLE / ADD CONSTRAINT: Unable to reference temporary table from permanent table constraint.");

				/*
				 * Grab an exclusive lock on the pk table, so that someone
				 * doesn't delete rows out from under us.
				 */

				pkrel = heap_openr(fkconstraint->pktable_name, AccessExclusiveLock);
				if (pkrel->rd_rel->relkind != RELKIND_RELATION)
					elog(ERROR, "referenced table \"%s\" not a relation",
						 fkconstraint->pktable_name);

				/*
				 * Grab an exclusive lock on the fk table, and then scan
				 * through each tuple, calling the RI_FKey_Match_Ins
				 * (insert trigger) as if that tuple had just been
				 * inserted.  If any of those fail, it should elog(ERROR)
				 * and that's that.
				 */
				rel = heap_openr(relationName, AccessExclusiveLock);
				if (rel->rd_rel->relkind != RELKIND_RELATION)
					elog(ERROR, "referencing table \"%s\" not a relation",
						 relationName);

				/*
				 * First we check for limited correctness of the
				 * constraint
				 */

				rel_attrs = pkrel->rd_att->attrs;
				indexoidlist = RelationGetIndexList(pkrel);

				foreach(indexoidscan, indexoidlist)
				{
					Oid			indexoid = lfirsti(indexoidscan);
					HeapTuple	indexTuple;
					Form_pg_index indexStruct;

					indexTuple = SearchSysCache(INDEXRELID,
											  ObjectIdGetDatum(indexoid),
												0, 0, 0);
					if (!HeapTupleIsValid(indexTuple))
						elog(ERROR, "transformFkeyGetPrimaryKey: index %u not found",
							 indexoid);
					indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);

					if (indexStruct->indisunique)
					{
						List	   *attrl;

						/*
						 * Make sure this index has the same number of
						 * keys -- It obviously won't match otherwise.
						 */
						for (i = 0; i < INDEX_MAX_KEYS && indexStruct->indkey[i] != 0; i++);
						if (i != length(fkconstraint->pk_attrs))
							found = false;
						else
						{
							attloc=0;
							/* go through the fkconstraint->pk_attrs list */
							foreach(attrl, fkconstraint->pk_attrs)
							{
								Ident	   *attr = lfirst(attrl);

								found = false;
								for (i = 0; i < INDEX_MAX_KEYS && indexStruct->indkey[i] != 0; i++)
								{
									int			pkattno = indexStruct->indkey[i];

									if (pkattno > 0)
									{
										char	   *name = NameStr(rel_attrs[pkattno - 1]->attname);

										if (strcmp(name, attr->name) == 0)
										{
											/* We get the type of this attribute here and
											 * store it so we can use it later for making
											 * sure the types are comparable.
											 */
											pktypoid[attloc++]=rel_attrs[pkattno-1]->atttypid;
											found = true;
											break;
										}
									}
								}
								if (!found)
									break;
							}
						}
					}
					ReleaseSysCache(indexTuple);
					if (found)
						break;
				}

				if (!found)
					elog(ERROR, "UNIQUE constraint matching given keys for referenced table \"%s\" not found",
						 fkconstraint->pktable_name);

				freeList(indexoidlist);
				heap_close(pkrel, NoLock);

				rel_attrs = rel->rd_att->attrs;
				if (fkconstraint->fk_attrs != NIL)
				{
					List	   *fkattrs;
					Ident	   *fkattr;

					found = false;
					attloc = 0;
					foreach(fkattrs, fkconstraint->fk_attrs)
					{
						int			count;

						found = false;
						fkattr = lfirst(fkattrs);
						for (count = 0; count < rel->rd_att->natts; count++)
						{
							char	   *name = NameStr(rel->rd_att->attrs[count]->attname);

							if (strcmp(name, fkattr->name) == 0)
							{
								/*
								 * Here once again we get the types, this
								 * time for the fk table's attributes
								 */
								fktypoid[attloc++]=rel->rd_att->attrs[count]->atttypid;
								found = true;
								break;
							}
						}
						if (!found)
							break;
					}
					if (!found)
						elog(ERROR, "columns referenced in foreign key constraint not found.");
				}

				for (i=0; i < INDEX_MAX_KEYS && fktypoid[i] !=0; i++) {
					/*
					 * fktypoid[i] is the foreign key table's i'th element's type oid
					 * pktypoid[i] is the primary key table's i'th element's type oid
					 * We let oper() do our work for us, including elog(ERROR) if the
					 * types can't compare with =
					 */
					Operator o=oper("=", fktypoid[i], pktypoid[i], false);
					ReleaseSysCache(o);
				}

				trig.tgoid = 0;
				if (fkconstraint->constr_name)
					trig.tgname = fkconstraint->constr_name;
				else
					trig.tgname = "<unknown>";
				trig.tgfoid = 0;
				trig.tgtype = 0;
				trig.tgenabled = TRUE;
				trig.tgisconstraint = TRUE;
				trig.tginitdeferred = FALSE;
				trig.tgdeferrable = FALSE;

				trig.tgargs = (char **) palloc(
					 sizeof(char *) * (4 + length(fkconstraint->fk_attrs)
									   + length(fkconstraint->pk_attrs)));

				if (fkconstraint->constr_name)
					trig.tgargs[0] = fkconstraint->constr_name;
				else
					trig.tgargs[0] = "<unknown>";
				trig.tgargs[1] = (char *) relationName;
				trig.tgargs[2] = fkconstraint->pktable_name;
				trig.tgargs[3] = fkconstraint->match_type;
				count = 4;
				foreach(list, fkconstraint->fk_attrs)
				{
					Ident	   *fk_at = lfirst(list);

					trig.tgargs[count] = fk_at->name;
					count += 2;
				}
				count = 5;
				foreach(list, fkconstraint->pk_attrs)
				{
					Ident	   *pk_at = lfirst(list);

					trig.tgargs[count] = pk_at->name;
					count += 2;
				}
				trig.tgnargs = count - 1;

				scan = heap_beginscan(rel, false, SnapshotNow, 0, NULL);
				AssertState(scan != NULL);

				while (HeapTupleIsValid(tuple = heap_getnext(scan, 0)))
				{
					/* Make a call to the check function */
					/* No parameters are passed, but we do set a context */
					FunctionCallInfoData fcinfo;
					TriggerData trigdata;

					MemSet(&fcinfo, 0, sizeof(fcinfo));
					/* We assume RI_FKey_check_ins won't look at flinfo... */

					trigdata.type = T_TriggerData;
					trigdata.tg_event = TRIGGER_EVENT_INSERT | TRIGGER_EVENT_ROW;
					trigdata.tg_relation = rel;
					trigdata.tg_trigtuple = tuple;
					trigdata.tg_newtuple = NULL;
					trigdata.tg_trigger = &trig;

					fcinfo.context = (Node *) &trigdata;

					RI_FKey_check_ins(&fcinfo);
				}
				heap_endscan(scan);
				heap_close(rel, NoLock);		/* close rel but keep
												 * lock! */

				pfree(trig.tgargs);
				break;
			}
		default:
			elog(ERROR, "ALTER TABLE / ADD CONSTRAINT unable to determine type of constraint passed");
	}
}



/*
 * ALTER TABLE DROP CONSTRAINT
 * Note: It is legal to remove a constraint with name "" as it is possible
 * to add a constraint with name "".
 * Christopher Kings-Lynne
 */
void
AlterTableDropConstraint(const char *relationName,
						 bool inh, const char *constrName,
						 int behavior)
{
	Relation		rel;
	int			deleted;

#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	/* We don't support CASCADE yet  - in fact, RESTRICT
	 * doesn't work to the spec either! */
	if (behavior == CASCADE)
		elog(ERROR, "ALTER TABLE / DROP CONSTRAINT does not support the CASCADE keyword");

	/*
	 * Acquire an exclusive lock on the target relation for
	 * the duration of the operation.
	 */

	rel = heap_openr(relationName, AccessExclusiveLock);

	/* Disallow DROP CONSTRAINT on views, indexes, sequences, etc */
	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE / DROP CONSTRAINT: %s is not a table",
			 relationName);

	/*
	 * Since all we have is the name of the constraint, we have to look through
	 * all catalogs that could possibly contain a constraint for this relation.
	 * We also keep a count of the number of constraints removed.
	 */

	deleted = 0;

	/*
	 * First, we remove all CHECK constraints with the given name
	 */

	deleted += RemoveCheckConstraint(rel, constrName, inh);

	/*
	 * Now we remove NULL, UNIQUE, PRIMARY KEY and FOREIGN KEY constraints.
	 *
	 * Unimplemented.
	 */

	/* Close the target relation */
	heap_close(rel, NoLock);

	/* If zero constraints deleted, complain */
	if (deleted == 0)
		elog(ERROR, "ALTER TABLE / DROP CONSTRAINT: %s does not exist",
			 constrName);
	/* Otherwise if more than one constraint deleted, notify */
	else if (deleted > 1)
		elog(NOTICE, "Multiple constraints dropped");

}


/*
 * ALTER TABLE OWNER
 */
void
AlterTableOwner(const char *relationName, const char *newOwnerName)
{
	Relation	class_rel;
	HeapTuple	tuple;
	int32		newOwnerSysid;
	Relation	idescs[Num_pg_class_indices];

	/*
	 * first check that we are a superuser
	 */
	if (!superuser())
		elog(ERROR, "ALTER TABLE: permission denied");

	/*
	 * look up the new owner in pg_shadow and get the sysid
	 */
	newOwnerSysid = get_usesysid(newOwnerName);

	/*
	 * find the table's entry in pg_class and make a modifiable copy
	 */
	class_rel = heap_openr(RelationRelationName, RowExclusiveLock);

	tuple = SearchSysCacheCopy(RELNAME,
							   PointerGetDatum(relationName),
							   0, 0, 0);
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "ALTER TABLE: relation \"%s\" not found",
			 relationName);

	switch (((Form_pg_class) GETSTRUCT(tuple))->relkind)
	{
		case RELKIND_RELATION:
		case RELKIND_INDEX:
		case RELKIND_VIEW:
		case RELKIND_SEQUENCE:
			/* ok to change owner */
			break;
		default:
			elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table, index, view, or sequence",
				 relationName);
	}

	/*
	 * modify the table's entry and write to the heap
	 */
	((Form_pg_class) GETSTRUCT(tuple))->relowner = newOwnerSysid;

	simple_heap_update(class_rel, &tuple->t_self, tuple);

	/* Keep the catalog indices up to date */
	CatalogOpenIndices(Num_pg_class_indices, Name_pg_class_indices, idescs);
	CatalogIndexInsert(idescs, Num_pg_class_indices, class_rel, tuple);
	CatalogCloseIndices(Num_pg_class_indices, idescs);

	/*
	 * unlock everything and return
	 */
	heap_freetuple(tuple);
	heap_close(class_rel, NoLock);
}


/*
 * ALTER TABLE CREATE TOAST TABLE
 */
void
AlterTableCreateToastTable(const char *relationName, bool silent)
{
	Relation	rel;
	Oid			myrelid;
	HeapTuple	reltup;
	HeapTupleData classtuple;
	TupleDesc	tupdesc;
	Relation	class_rel;
	Buffer		buffer;
	Relation	ridescs[Num_pg_class_indices];
	Oid			toast_relid;
	Oid			toast_idxid;
	char		toast_relname[NAMEDATALEN + 1];
	char		toast_idxname[NAMEDATALEN + 1];
	Relation	toast_idxrel;
	IndexInfo  *indexInfo;
	Oid			classObjectId[1];

	/*
	 * permissions checking.  XXX exactly what is appropriate here?
	 */
#ifndef NO_SECURITY
	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
		elog(ERROR, "ALTER TABLE: permission denied");
#endif

	/*
	 * Grab an exclusive lock on the target table, which we will NOT
	 * release until end of transaction.
	 */
	rel = heap_openr(relationName, AccessExclusiveLock);

	if (rel->rd_rel->relkind != RELKIND_RELATION)
		elog(ERROR, "ALTER TABLE: relation \"%s\" is not a table",
			 relationName);

	myrelid = RelationGetRelid(rel);

	/*
	 * lock the pg_class tuple for update (is that really needed?)
	 */
	class_rel = heap_openr(RelationRelationName, RowExclusiveLock);

	reltup = SearchSysCache(RELNAME,
							PointerGetDatum(relationName),
							0, 0, 0);
	if (!HeapTupleIsValid(reltup))
		elog(ERROR, "ALTER TABLE: relation \"%s\" not found",
			 relationName);
	classtuple.t_self = reltup->t_self;
	ReleaseSysCache(reltup);

	switch (heap_mark4update(class_rel, &classtuple, &buffer))
	{
		case HeapTupleSelfUpdated:
		case HeapTupleMayBeUpdated:
			break;
		default:
			elog(ERROR, "couldn't lock pg_class tuple");
	}
	reltup = heap_copytuple(&classtuple);
	ReleaseBuffer(buffer);

	/*
	 * Is it already toasted?
	 */
	if (((Form_pg_class) GETSTRUCT(reltup))->reltoastrelid != InvalidOid)
	{
		if (silent)
		{
			heap_close(rel, NoLock);
			heap_close(class_rel, NoLock);
			heap_freetuple(reltup);
			return;
		}

		elog(ERROR, "ALTER TABLE: relation \"%s\" already has a toast table",
			 relationName);
	}

	/*
	 * Check to see whether the table actually needs a TOAST table.
	 */
	if (!needs_toast_table(rel))
	{
		if (silent)
		{
			heap_close(rel, NoLock);
			heap_close(class_rel, NoLock);
			heap_freetuple(reltup);
			return;
		}

		elog(ERROR, "ALTER TABLE: relation \"%s\" does not need a toast table",
			 relationName);
	}

	/*
	 * Create the toast table and its index
	 */
	sprintf(toast_relname, "pg_toast_%u", myrelid);
	sprintf(toast_idxname, "pg_toast_%u_idx", myrelid);

	/* this is pretty painful...  need a tuple descriptor */
	tupdesc = CreateTemplateTupleDesc(3);
	TupleDescInitEntry(tupdesc, (AttrNumber) 1,
					   "chunk_id",
					   OIDOID,
					   -1, 0, false);
	TupleDescInitEntry(tupdesc, (AttrNumber) 2,
					   "chunk_seq",
					   INT4OID,
					   -1, 0, false);
	TupleDescInitEntry(tupdesc, (AttrNumber) 3,
					   "chunk_data",
					   BYTEAOID,
					   -1, 0, false);

	/*
	 * Ensure that the toast table doesn't itself get toasted, or we'll be
	 * toast :-(.  This is essential for chunk_data because type bytea is
	 * toastable; hit the other two just to be sure.
	 */
	tupdesc->attrs[0]->attstorage = 'p';
	tupdesc->attrs[1]->attstorage = 'p';
	tupdesc->attrs[2]->attstorage = 'p';

	/*
	 * Note: the toast relation is considered a "normal" relation even if
	 * its master relation is a temp table.  There cannot be any naming
	 * collision, and the toast rel will be destroyed when its master is,
	 * so there's no need to handle the toast rel as temp.
	 */
	toast_relid = heap_create_with_catalog(toast_relname, tupdesc,
										   RELKIND_TOASTVALUE,
										   false, true);

	/* make the toast relation visible, else index creation will fail */
	CommandCounterIncrement();

	/* create index on chunk_id */

	indexInfo = makeNode(IndexInfo);
	indexInfo->ii_NumIndexAttrs = 1;
	indexInfo->ii_NumKeyAttrs = 1;
	indexInfo->ii_KeyAttrNumbers[0] = 1;
	indexInfo->ii_Predicate = NIL;
	indexInfo->ii_FuncOid = InvalidOid;
	indexInfo->ii_Unique = false;

	classObjectId[0] = OID_OPS_OID;

	index_create(toast_relname, toast_idxname, indexInfo,
				 BTREE_AM_OID, classObjectId,
				 false, false, true);

	/*
	 * Update toast rel's pg_class entry to show that it has an index.
	 */
	setRelhasindex(toast_relid, true);

	/*
	 * Make index visible
	 */
	CommandCounterIncrement();

	/*
	 * Get the OID of the newly created index
	 */
	toast_idxrel = index_openr(toast_idxname);
	toast_idxid = RelationGetRelid(toast_idxrel);
	index_close(toast_idxrel);

	/*
	 * Store the toast table- and index-Oid's in the relation tuple
	 */
	((Form_pg_class) GETSTRUCT(reltup))->reltoastrelid = toast_relid;
	((Form_pg_class) GETSTRUCT(reltup))->reltoastidxid = toast_idxid;
	simple_heap_update(class_rel, &reltup->t_self, reltup);

	/*
	 * Keep catalog indices current
	 */
	CatalogOpenIndices(Num_pg_class_indices, Name_pg_class_indices, ridescs);
	CatalogIndexInsert(ridescs, Num_pg_class_indices, class_rel, reltup);
	CatalogCloseIndices(Num_pg_class_indices, ridescs);

	heap_freetuple(reltup);

	/*
	 * Close relations and make changes visible
	 */
	heap_close(class_rel, NoLock);
	heap_close(rel, NoLock);

	CommandCounterIncrement();
}

/*
 * Check to see whether the table needs a TOAST table.	It does only if
 * (1) there are any toastable attributes, and (2) the maximum length
 * of a tuple could exceed TOAST_TUPLE_THRESHOLD.  (We don't want to
 * create a toast table for something like "f1 varchar(20)".)
 */
static bool
needs_toast_table(Relation rel)
{
	int32		data_length = 0;
	bool		maxlength_unknown = false;
	bool		has_toastable_attrs = false;
	TupleDesc	tupdesc;
	Form_pg_attribute *att;
	int32		tuple_length;
	int			i;

	tupdesc = rel->rd_att;
	att = tupdesc->attrs;

	for (i = 0; i < tupdesc->natts; i++)
	{
		data_length = att_align(data_length, att[i]->attlen, att[i]->attalign);
		if (att[i]->attlen >= 0)
		{
			/* Fixed-length types are never toastable */
			data_length += att[i]->attlen;
		}
		else
		{
			int32		maxlen = type_maximum_size(att[i]->atttypid,
												   att[i]->atttypmod);

			if (maxlen < 0)
				maxlength_unknown = true;
			else
				data_length += maxlen;
			if (att[i]->attstorage != 'p')
				has_toastable_attrs = true;
		}
	}
	if (!has_toastable_attrs)
		return false;			/* nothing to toast? */
	if (maxlength_unknown)
		return true;			/* any unlimited-length attrs? */
	tuple_length = MAXALIGN(offsetof(HeapTupleHeaderData, t_bits) +
							BITMAPLEN(tupdesc->natts)) +
		MAXALIGN(data_length);
	return (tuple_length > TOAST_TUPLE_THRESHOLD);
}
	
/*
 *
 * LOCK TABLE
 *
 */
void
LockTableCommand(LockStmt *lockstmt)
{
	List *p;
	Relation rel;
	
	/* Iterate over the list and open, lock, and close the relations
	   one at a time
	 */

		foreach(p, lockstmt->rellist)
		{
			char* relname = strVal(lfirst(p));
			int			aclresult;
			
			rel = heap_openr(relname, NoLock);

			if (rel->rd_rel->relkind != RELKIND_RELATION)
				elog(ERROR, "LOCK TABLE: %s is not a table", 
					 relname);
			
			if (lockstmt->mode == AccessShareLock)
				aclresult = pg_aclcheck(relname, GetUserId(),
										ACL_SELECT);
			else
				aclresult = pg_aclcheck(relname, GetUserId(),
										ACL_UPDATE | ACL_DELETE);

			if (aclresult != ACLCHECK_OK)
				elog(ERROR, "LOCK TABLE: permission denied");

			LockRelation(rel, lockstmt->mode);
			
			heap_close(rel, NoLock);	/* close rel, keep lock */
		}
}


static bool
is_relation(char *name)
{
	Relation	rel = heap_openr(name, NoLock);

	bool		retval = (rel->rd_rel->relkind == RELKIND_RELATION);

	heap_close(rel, NoLock);

	return retval;
}