src/backend/catalog/pg_attribute_encoding.c - cloudberry - Git at Google

 /*-------------------------------------------------------------------------
  *
  * pg_attribute_encoding.c
  *	  Routines to manipulation and retrieve column encoding information.
  *
  * Portions Copyright (c) EMC, 2011
  * Portions Copyright (c) 2012-Present VMware, Inc. or its affiliates.
  *
  *
  * IDENTIFICATION
  *	    src/backend/catalog/pg_attribute_encoding.c
  *
  *-------------------------------------------------------------------------
  */

 #include "postgres.h"

 #include "access/genam.h"
 #include "access/heapam.h"
 #include "access/htup_details.h"
 #include "access/reloptions.h"
 #include "access/xact.h"
 #include "catalog/indexing.h"
 #include "catalog/pg_attribute_encoding.h"
 #include "catalog/pg_compression.h"
 #include "catalog/dependency.h"
 #include "fmgr.h"
 #include "parser/analyze.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
 #include "utils/fmgroids.h"
 #include "utils/formatting.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
 #include "utils/relcache.h"
 #include "utils/syscache.h"

 #include "catalog/gp_indexing.h"

 /*
  * Add a single attribute encoding entry.
  */
 static void
 add_attribute_encoding_entry(Oid relid, AttrNumber attnum, FileNumber filenum, Datum attoptions)
 {
 	Relation	rel;
 	Datum values[Natts_pg_attribute_encoding];
 	bool nulls[Natts_pg_attribute_encoding];
 	HeapTuple tuple;

 	Assert(attnum != InvalidAttrNumber);
 	Assert(filenum != InvalidFileNumber);

 	rel = heap_open(AttributeEncodingRelationId, RowExclusiveLock);

 	MemSet(nulls, 0, sizeof(nulls));
 	values[Anum_pg_attribute_encoding_attrelid - 1] = ObjectIdGetDatum(relid);
 	values[Anum_pg_attribute_encoding_attnum - 1] = Int16GetDatum(attnum);
 	values[Anum_pg_attribute_encoding_filenum - 1] = Int16GetDatum(filenum);
 	values[Anum_pg_attribute_encoding_attoptions - 1] = attoptions;

 	tuple = heap_form_tuple(RelationGetDescr(rel), values, nulls);

 	/* insert a new tuple */
 	CatalogTupleInsert(rel, tuple);

 	heap_freetuple(tuple);

 	heap_close(rel, RowExclusiveLock);
 }

 /*
  * Get the set of functions implementing a compression algorithm.
  *
  * Intercept requests for "none", since that is not a real compression
  * implementation but a fake one to indicate no compression desired.
  */
 PGFunction *
 get_funcs_for_compression(char *compresstype)
 {
 	PGFunction *func = NULL;

 	if (compresstype == NULL ||
 		compresstype[0] == '\0' ||
 		pg_strcasecmp("none", compresstype) == 0)
 	{
 		return func;
 	}
 	else
 	{
 		func = GetCompressionImplementation(compresstype);

 		Assert(PointerIsValid(func));
 	}
 	return func;
 }

 /*
  * Get datum representations of the attoptions field in pg_attribute_encoding
  * for the given relation.
  */
 Datum *
 get_rel_attoptions(Oid relid, AttrNumber max_attno)
 {
 	HeapTuple 			atttuple;
 	Form_pg_attribute 		attform;
 	Datum				*dats;
 	CatCList 			*attenclist;

 	/* used for attbyval and len below */
 	atttuple = SearchSysCache2(ATTNUM,
 							ObjectIdGetDatum(AttributeEncodingRelationId),
 							Int16GetDatum(Anum_pg_attribute_encoding_attoptions));
 	attform = (Form_pg_attribute) GETSTRUCT(atttuple);

 	dats = palloc0(max_attno * sizeof(Datum));

 	attenclist = SearchSysCacheList1(ATTENCODINGNUM, relid);
 	for (int i = 0; i < attenclist->n_members; i++)
 	{
 		HeapTuple	tuple = &attenclist->members[i]->tuple;
 		Form_pg_attribute_encoding	form =
 					(Form_pg_attribute_encoding)GETSTRUCT(tuple);
 		AttrNumber 	attnum = form->attnum;
 		Datum 		attoptions;
 		bool 		isnull;

 		Assert(attnum > 0 && attnum <= max_attno);

 		attoptions = SysCacheGetAttr(ATTENCODINGNUM, tuple, Anum_pg_attribute_encoding_attoptions,
                                                                    &isnull);
 		if (!isnull)
 			dats[attnum - 1] = datumCopy(attoptions,
 										 attform->attbyval,
 										 attform->attlen);
 	}
 	ReleaseSysCacheList(attenclist);

 	ReleaseSysCache(atttuple);

 	return dats;

 }

 /*
  * Given a relation, get all column encodings for that relation as a list of
  * ColumnReferenceStorageDirective structures.
  */
 List *
 rel_get_column_encodings(Relation rel)
 {
 	List **colencs = RelationGetUntransformedAttributeOptions(rel);
 	List *out = NIL;

 	if (colencs)
 	{
 		AttrNumber attno;

 		for (attno = 0; attno < RelationGetNumberOfAttributes(rel); attno++)
 		{
 			if (colencs[attno] && !TupleDescAttr(rel->rd_att, attno)->attisdropped)
 			{
 				ColumnReferenceStorageDirective *d =
 					makeNode(ColumnReferenceStorageDirective);
 				d->column = pstrdup(NameStr(TupleDescAttr(rel->rd_att, attno)->attname));
 				d->encoding = colencs[attno];

 				out = lappend(out, d);
 			}
 		}
 	}
 	return out;
 }

 /*
  * Add pg_attribute_encoding entries for newrelid. Make them identical to those
  * stored for oldrelid.
  */
 void
 cloneAttributeEncoding(Oid oldrelid, Oid newrelid, AttrNumber max_attno)
 {
 	Datum *attoptions = get_rel_attoptions(oldrelid, max_attno);
 	AttrNumber n;

 	for (n = 0; n < max_attno; n++)
 	{
 		if (DatumGetPointer(attoptions[n]) != NULL)
 			add_attribute_encoding_entry(newrelid,
 										 n + 1,
 										 n + 1,
 										 attoptions[n]);
 	}
 	CommandCounterIncrement();
 }

 List **
 RelationGetUntransformedAttributeOptions(Relation rel)
 {
 	List **l;
 	int i;
 	Datum *dats = get_rel_attoptions(RelationGetRelid(rel),
 									 RelationGetNumberOfAttributes(rel));

 	l = palloc0(RelationGetNumberOfAttributes(rel) * sizeof(List *));

 	for (i = 0; i < RelationGetNumberOfAttributes(rel); i++)
 	{
 		l[i] = untransformRelOptions(dats[i]);
 	}

 	return l;
 }

 /*
  * Get all storage options for all user attributes of the table.
  */
 StdRdOptions **
 RelationGetAttributeOptions(Relation rel)
 {
 	Datum *dats;
 	StdRdOptions **opts;
 	int i;
 	int	natts;

 	natts = RelationGetNumberOfAttributes(rel);

 	opts = palloc0(natts * sizeof(StdRdOptions *));

 	dats = get_rel_attoptions(RelationGetRelid(rel),
 							  natts);

 	for (i = 0; i < natts; i++)
 	{
 		if (DatumGetPointer(dats[i]) != NULL)
 		{
 			opts[i] = (StdRdOptions *) default_reloptions(
 					dats[i], false,
 					RELOPT_KIND_APPENDOPTIMIZED);
 			pfree(DatumGetPointer(dats[i]));
 		}
 	}
 	pfree(dats);

 	return opts;
 }

 /*
  * Work horse underneath DefineRelation().
  *
  * Simply adds user specified ENCODING () clause information to
  * pg_attribute_encoding. Should be absolutely valid at this point.
  *
  * Note that we need to take dropped columns into consideration
  * as well so we cannot use get_attnum().
  */
 void
 AddRelationAttributeEncodings(Relation rel, List *attr_encodings)
 {
 	if (!attr_encodings)
 		return;
 	Oid relid = RelationGetRelid(rel);
 	ListCell *lc;
 	ListCell *lc_filenum;
 	List *filenums = GetNextNAvailableFilenums(relid, attr_encodings->length);

 	if (filenums->length != attr_encodings->length)
 		ereport(ERROR,
 				(errcode(ERRCODE_INTERNAL_ERROR),
 					errmsg("filenums exhausted for relid %u", relid),
 					errhint("recreate the table")));

 	forboth(lc, attr_encodings, lc_filenum, filenums)
 	{
 		Datum attoptions;
 		ColumnReferenceStorageDirective *c = lfirst(lc);
 		List *encoding;
 		AttrNumber attnum;
 		HeapTuple	tuple;
 		Form_pg_attribute att_tup;

 		Assert(IsA(c, ColumnReferenceStorageDirective));

 		tuple = SearchSysCache2(ATTNAME,
 								ObjectIdGetDatum(relid),
 								CStringGetDatum(c->column));
 		if (!HeapTupleIsValid(tuple))
 			elog(ERROR, "column \"%s\" does not exist", c->column);

 		att_tup = (Form_pg_attribute) GETSTRUCT(tuple);
 		attnum = att_tup->attnum;
 		Assert(attnum != InvalidAttrNumber);

 		ReleaseSysCache(tuple);

 		if (attnum < 0)
 			elog(ERROR, "column \"%s\" is a system column", c->column);

 		encoding = c->encoding;

 		if (!encoding)
 			continue;

 		attoptions = transformRelOptions(PointerGetDatum(NULL),
 										 encoding,
 										 NULL,
 										 NULL,
 										 true,
 										 false);

 		add_attribute_encoding_entry(relid, attnum, lfirst_int(lc_filenum), attoptions);
 	}
 	list_free(filenums);
 }

 void
 RemoveAttributeEncodingsByRelid(Oid relid)
 {
 	Relation	rel;
 	ScanKeyData skey;
 	SysScanDesc scan;
 	HeapTuple	tup;

 	rel = heap_open(AttributeEncodingRelationId, RowExclusiveLock);

 	ScanKeyInit(&skey,
 				Anum_pg_attribute_encoding_attrelid,
 				BTEqualStrategyNumber, F_OIDEQ,
 				ObjectIdGetDatum(relid));
 	scan = systable_beginscan(rel, AttributeEncodingAttrelidIndexId, true,
 							  NULL, 1, &skey);
 	while (HeapTupleIsValid(tup = systable_getnext(scan)))
 	{
 		simple_heap_delete(rel, &tup->t_self);
 	}

 	systable_endscan(scan);

 	heap_close(rel, RowExclusiveLock);
 }

 /*
  * Returns the filenum value for a relation/attnum entry in pg_attribute_encoding
  */
 FileNumber
 GetFilenumForAttribute(Oid relid, AttrNumber attnum)
 {
 	HeapTuple	tup;
 	FileNumber  filenum;
 	bool        isnull;

 	Assert(OidIsValid(relid));
 	Assert(AttributeNumberIsValid(attnum));

 	tup = SearchSysCache2(ATTENCODINGNUM,
 							ObjectIdGetDatum(relid),
 							Int16GetDatum(attnum));
 	if (!HeapTupleIsValid(tup))
 		ereport(ERROR,
 				(errcode(ERRCODE_INTERNAL_ERROR),
 					errmsg("unable to find pg_attribute_encoding entry for attribute %d of relation %u",
 								attnum, relid)));

 	filenum = SysCacheGetAttr(ATTENCODINGNUM,
 							tup,
 							Anum_pg_attribute_encoding_filenum,
 							&isnull);
 	Assert(!isnull);
 	ReleaseSysCache(tup);
 	return filenum;
 }

 /*
  * Returns a sorted list of first n unused filenums in pg_attribute_encoding
  * for the relation
  * In the outside chance that filenums have been exhausted,
  * the list may contain < n unused filenums
  */
 List *
 GetNextNAvailableFilenums(Oid relid, int n)
 {
 	Relation    rel;
 	SysScanDesc scan;
 	ScanKeyData skey[1];
 	HeapTuple	tup;
 	bool        isnull;
 	bool        used[MaxFileNumber];
 	List        *newfilenums = NIL;

 	Assert(OidIsValid(relid));

 	MemSet(used, false, sizeof(used));
 	rel = heap_open(AttributeEncodingRelationId, AccessShareLock);

 	ScanKeyInit(&skey[0],
 				Anum_pg_attribute_encoding_attrelid,
 				BTEqualStrategyNumber, F_OIDEQ,
 				ObjectIdGetDatum(relid));
 	scan = systable_beginscan(rel, AttributeEncodingAttrelidIndexId, true,
 							  NULL, 1, skey);

 	while (HeapTupleIsValid(tup = systable_getnext(scan)))
 	{
 		FileNumber usedfilenum = heap_getattr(tup, Anum_pg_attribute_encoding_filenum,
 							   RelationGetDescr(rel), &isnull);
 		Assert(!isnull);
 		used[usedfilenum-1] = true;
 	}

 	systable_endscan(scan);
 	heap_close(rel, AccessShareLock);

 	for (int i = 0; i < MaxFileNumber; ++i)
 	{
 		if(!used[i])
 		{
 			newfilenums = lappend_int(newfilenums, i + 1);
 			if (newfilenums->length == n)
 				break;
 		}
 	}
 	return newfilenums;
 }
	/*-------------------------------------------------------------------------
	*
	* pg_attribute_encoding.c
	* Routines to manipulation and retrieve column encoding information.
	*
	* Portions Copyright (c) EMC, 2011
	* Portions Copyright (c) 2012-Present VMware, Inc. or its affiliates.
	*
	*
	* IDENTIFICATION
	* src/backend/catalog/pg_attribute_encoding.c
	*
	*-------------------------------------------------------------------------
	*/

	#include "postgres.h"

	#include "access/genam.h"
	#include "access/heapam.h"
	#include "access/htup_details.h"
	#include "access/reloptions.h"
	#include "access/xact.h"
	#include "catalog/indexing.h"
	#include "catalog/pg_attribute_encoding.h"
	#include "catalog/pg_compression.h"
	#include "catalog/dependency.h"
	#include "fmgr.h"
	#include "parser/analyze.h"
	#include "utils/builtins.h"
	#include "utils/datum.h"
	#include "utils/fmgroids.h"
	#include "utils/formatting.h"
	#include "utils/lsyscache.h"
	#include "utils/rel.h"
	#include "utils/relcache.h"
	#include "utils/syscache.h"

	#include "catalog/gp_indexing.h"

	/*
	* Add a single attribute encoding entry.
	*/
	static void
	add_attribute_encoding_entry(Oid relid, AttrNumber attnum, FileNumber filenum, Datum attoptions)
	{
	Relation rel;
	Datum values[Natts_pg_attribute_encoding];
	bool nulls[Natts_pg_attribute_encoding];
	HeapTuple tuple;

	Assert(attnum != InvalidAttrNumber);
	Assert(filenum != InvalidFileNumber);

	rel = heap_open(AttributeEncodingRelationId, RowExclusiveLock);

	MemSet(nulls, 0, sizeof(nulls));
	values[Anum_pg_attribute_encoding_attrelid - 1] = ObjectIdGetDatum(relid);
	values[Anum_pg_attribute_encoding_attnum - 1] = Int16GetDatum(attnum);
	values[Anum_pg_attribute_encoding_filenum - 1] = Int16GetDatum(filenum);
	values[Anum_pg_attribute_encoding_attoptions - 1] = attoptions;

	tuple = heap_form_tuple(RelationGetDescr(rel), values, nulls);

	/* insert a new tuple */
	CatalogTupleInsert(rel, tuple);

	heap_freetuple(tuple);

	heap_close(rel, RowExclusiveLock);
	}

	/*
	* Get the set of functions implementing a compression algorithm.
	*
	* Intercept requests for "none", since that is not a real compression
	* implementation but a fake one to indicate no compression desired.
	*/
	PGFunction *
	get_funcs_for_compression(char *compresstype)
	{
	PGFunction *func = NULL;

	if (compresstype == NULL \|\|
	compresstype[0] == '\0' \|\|
	pg_strcasecmp("none", compresstype) == 0)
	{
	return func;
	}
	else
	{
	func = GetCompressionImplementation(compresstype);

	Assert(PointerIsValid(func));
	}
	return func;
	}

	/*
	* Get datum representations of the attoptions field in pg_attribute_encoding
	* for the given relation.
	*/
	Datum *
	get_rel_attoptions(Oid relid, AttrNumber max_attno)
	{
	HeapTuple atttuple;
	Form_pg_attribute attform;
	Datum *dats;
	CatCList *attenclist;

	/* used for attbyval and len below */
	atttuple = SearchSysCache2(ATTNUM,
	ObjectIdGetDatum(AttributeEncodingRelationId),
	Int16GetDatum(Anum_pg_attribute_encoding_attoptions));
	attform = (Form_pg_attribute) GETSTRUCT(atttuple);

	dats = palloc0(max_attno * sizeof(Datum));

	attenclist = SearchSysCacheList1(ATTENCODINGNUM, relid);
	for (int i = 0; i < attenclist->n_members; i++)
	{
	HeapTuple tuple = &attenclist->members[i]->tuple;
	Form_pg_attribute_encoding form =
	(Form_pg_attribute_encoding)GETSTRUCT(tuple);
	AttrNumber attnum = form->attnum;
	Datum attoptions;
	bool isnull;

	Assert(attnum > 0 && attnum <= max_attno);

	attoptions = SysCacheGetAttr(ATTENCODINGNUM, tuple, Anum_pg_attribute_encoding_attoptions,
	&isnull);
	if (!isnull)
	dats[attnum - 1] = datumCopy(attoptions,
	attform->attbyval,
	attform->attlen);
	}
	ReleaseSysCacheList(attenclist);

	ReleaseSysCache(atttuple);

	return dats;

	}

	/*
	* Given a relation, get all column encodings for that relation as a list of
	* ColumnReferenceStorageDirective structures.
	*/
	List *
	rel_get_column_encodings(Relation rel)
	{
	List **colencs = RelationGetUntransformedAttributeOptions(rel);
	List *out = NIL;

	if (colencs)
	{
	AttrNumber attno;

	for (attno = 0; attno < RelationGetNumberOfAttributes(rel); attno++)
	{
	if (colencs[attno] && !TupleDescAttr(rel->rd_att, attno)->attisdropped)
	{
	ColumnReferenceStorageDirective *d =
	makeNode(ColumnReferenceStorageDirective);
	d->column = pstrdup(NameStr(TupleDescAttr(rel->rd_att, attno)->attname));
	d->encoding = colencs[attno];

	out = lappend(out, d);
	}
	}
	}
	return out;
	}

	/*
	* Add pg_attribute_encoding entries for newrelid. Make them identical to those
	* stored for oldrelid.
	*/
	void
	cloneAttributeEncoding(Oid oldrelid, Oid newrelid, AttrNumber max_attno)
	{
	Datum *attoptions = get_rel_attoptions(oldrelid, max_attno);
	AttrNumber n;

	for (n = 0; n < max_attno; n++)
	{
	if (DatumGetPointer(attoptions[n]) != NULL)
	add_attribute_encoding_entry(newrelid,
	n + 1,
	n + 1,
	attoptions[n]);
	}
	CommandCounterIncrement();
	}

	List **
	RelationGetUntransformedAttributeOptions(Relation rel)
	{
	List **l;
	int i;
	Datum *dats = get_rel_attoptions(RelationGetRelid(rel),
	RelationGetNumberOfAttributes(rel));

	l = palloc0(RelationGetNumberOfAttributes(rel) * sizeof(List *));

	for (i = 0; i < RelationGetNumberOfAttributes(rel); i++)
	{
	l[i] = untransformRelOptions(dats[i]);
	}

	return l;
	}

	/*
	* Get all storage options for all user attributes of the table.
	*/
	StdRdOptions **
	RelationGetAttributeOptions(Relation rel)
	{
	Datum *dats;
	StdRdOptions **opts;
	int i;
	int natts;

	natts = RelationGetNumberOfAttributes(rel);

	opts = palloc0(natts * sizeof(StdRdOptions *));

	dats = get_rel_attoptions(RelationGetRelid(rel),
	natts);

	for (i = 0; i < natts; i++)
	{
	if (DatumGetPointer(dats[i]) != NULL)
	{
	opts[i] = (StdRdOptions *) default_reloptions(
	dats[i], false,
	RELOPT_KIND_APPENDOPTIMIZED);
	pfree(DatumGetPointer(dats[i]));
	}
	}
	pfree(dats);

	return opts;
	}

	/*
	* Work horse underneath DefineRelation().
	*
	* Simply adds user specified ENCODING () clause information to
	* pg_attribute_encoding. Should be absolutely valid at this point.
	*
	* Note that we need to take dropped columns into consideration
	* as well so we cannot use get_attnum().
	*/
	void
	AddRelationAttributeEncodings(Relation rel, List *attr_encodings)
	{
	if (!attr_encodings)
	return;
	Oid relid = RelationGetRelid(rel);
	ListCell *lc;
	ListCell *lc_filenum;
	List *filenums = GetNextNAvailableFilenums(relid, attr_encodings->length);

	if (filenums->length != attr_encodings->length)
	ereport(ERROR,
	(errcode(ERRCODE_INTERNAL_ERROR),
	errmsg("filenums exhausted for relid %u", relid),
	errhint("recreate the table")));

	forboth(lc, attr_encodings, lc_filenum, filenums)
	{
	Datum attoptions;
	ColumnReferenceStorageDirective *c = lfirst(lc);
	List *encoding;
	AttrNumber attnum;
	HeapTuple tuple;
	Form_pg_attribute att_tup;

	Assert(IsA(c, ColumnReferenceStorageDirective));

	tuple = SearchSysCache2(ATTNAME,
	ObjectIdGetDatum(relid),
	CStringGetDatum(c->column));
	if (!HeapTupleIsValid(tuple))
	elog(ERROR, "column \"%s\" does not exist", c->column);

	att_tup = (Form_pg_attribute) GETSTRUCT(tuple);
	attnum = att_tup->attnum;
	Assert(attnum != InvalidAttrNumber);

	ReleaseSysCache(tuple);

	if (attnum < 0)
	elog(ERROR, "column \"%s\" is a system column", c->column);

	encoding = c->encoding;

	if (!encoding)
	continue;

	attoptions = transformRelOptions(PointerGetDatum(NULL),
	encoding,
	NULL,
	NULL,
	true,
	false);

	add_attribute_encoding_entry(relid, attnum, lfirst_int(lc_filenum), attoptions);
	}
	list_free(filenums);
	}

	void
	RemoveAttributeEncodingsByRelid(Oid relid)
	{
	Relation rel;
	ScanKeyData skey;
	SysScanDesc scan;
	HeapTuple tup;

	rel = heap_open(AttributeEncodingRelationId, RowExclusiveLock);

	ScanKeyInit(&skey,
	Anum_pg_attribute_encoding_attrelid,
	BTEqualStrategyNumber, F_OIDEQ,
	ObjectIdGetDatum(relid));
	scan = systable_beginscan(rel, AttributeEncodingAttrelidIndexId, true,
	NULL, 1, &skey);
	while (HeapTupleIsValid(tup = systable_getnext(scan)))
	{
	simple_heap_delete(rel, &tup->t_self);
	}

	systable_endscan(scan);

	heap_close(rel, RowExclusiveLock);
	}

	/*
	* Returns the filenum value for a relation/attnum entry in pg_attribute_encoding
	*/
	FileNumber
	GetFilenumForAttribute(Oid relid, AttrNumber attnum)
	{
	HeapTuple tup;
	FileNumber filenum;
	bool isnull;

	Assert(OidIsValid(relid));
	Assert(AttributeNumberIsValid(attnum));

	tup = SearchSysCache2(ATTENCODINGNUM,
	ObjectIdGetDatum(relid),
	Int16GetDatum(attnum));
	if (!HeapTupleIsValid(tup))
	ereport(ERROR,
	(errcode(ERRCODE_INTERNAL_ERROR),
	errmsg("unable to find pg_attribute_encoding entry for attribute %d of relation %u",
	attnum, relid)));

	filenum = SysCacheGetAttr(ATTENCODINGNUM,
	tup,
	Anum_pg_attribute_encoding_filenum,
	&isnull);
	Assert(!isnull);
	ReleaseSysCache(tup);
	return filenum;
	}

	/*
	* Returns a sorted list of first n unused filenums in pg_attribute_encoding
	* for the relation
	* In the outside chance that filenums have been exhausted,
	* the list may contain < n unused filenums
	*/
	List *
	GetNextNAvailableFilenums(Oid relid, int n)
	{
	Relation rel;
	SysScanDesc scan;
	ScanKeyData skey[1];
	HeapTuple tup;
	bool isnull;
	bool used[MaxFileNumber];
	List *newfilenums = NIL;

	Assert(OidIsValid(relid));

	MemSet(used, false, sizeof(used));
	rel = heap_open(AttributeEncodingRelationId, AccessShareLock);

	ScanKeyInit(&skey[0],
	Anum_pg_attribute_encoding_attrelid,
	BTEqualStrategyNumber, F_OIDEQ,
	ObjectIdGetDatum(relid));
	scan = systable_beginscan(rel, AttributeEncodingAttrelidIndexId, true,
	NULL, 1, skey);

	while (HeapTupleIsValid(tup = systable_getnext(scan)))
	{
	FileNumber usedfilenum = heap_getattr(tup, Anum_pg_attribute_encoding_filenum,
	RelationGetDescr(rel), &isnull);
	Assert(!isnull);
	used[usedfilenum-1] = true;
	}

	systable_endscan(scan);
	heap_close(rel, AccessShareLock);

	for (int i = 0; i < MaxFileNumber; ++i)
	{
	if(!used[i])
	{
	newfilenums = lappend_int(newfilenums, i + 1);
	if (newfilenums->length == n)
	break;
	}
	}
	return newfilenums;
	}