path: root/src/backend/access/heap/heaptoast.c

/*-------------------------------------------------------------------------
 *
 * heaptoast.c
 *	  Heap-specific definitions for external and compressed storage
 *	  of variable size attributes.
 *
 * Copyright (c) 2000-2019, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *	  src/backend/access/heap/heaptoast.c
 *
 *
 * INTERFACE ROUTINES
 *		toast_insert_or_update -
 *			Try to make a given tuple fit into one page by compressing
 *			or moving off attributes
 *
 *		toast_delete -
 *			Reclaim toast storage when a tuple is deleted
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/detoast.h"
#include "access/heapam.h"
#include "access/heaptoast.h"
#include "access/toast_internals.h"


/* ----------
 * toast_delete -
 *
 *	Cascaded delete toast-entries on DELETE
 * ----------
 */
void
toast_delete(Relation rel, HeapTuple oldtup, bool is_speculative)
{
	TupleDesc	tupleDesc;
	int			numAttrs;
	int			i;
	Datum		toast_values[MaxHeapAttributeNumber];
	bool		toast_isnull[MaxHeapAttributeNumber];

	/*
	 * We should only ever be called for tuples of plain relations or
	 * materialized views --- recursing on a toast rel is bad news.
	 */
	Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
		   rel->rd_rel->relkind == RELKIND_MATVIEW);

	/*
	 * Get the tuple descriptor and break down the tuple into fields.
	 *
	 * NOTE: it's debatable whether to use heap_deform_tuple() here or just
	 * heap_getattr() only the varlena columns.  The latter could win if there
	 * are few varlena columns and many non-varlena ones. However,
	 * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
	 * O(N^2) if there are many varlena columns, so it seems better to err on
	 * the side of linear cost.  (We won't even be here unless there's at
	 * least one varlena column, by the way.)
	 */
	tupleDesc = rel->rd_att;
	numAttrs = tupleDesc->natts;

	Assert(numAttrs <= MaxHeapAttributeNumber);
	heap_deform_tuple(oldtup, tupleDesc, toast_values, toast_isnull);

	/*
	 * Check for external stored attributes and delete them from the secondary
	 * relation.
	 */
	for (i = 0; i < numAttrs; i++)
	{
		if (TupleDescAttr(tupleDesc, i)->attlen == -1)
		{
			Datum		value = toast_values[i];

			if (toast_isnull[i])
				continue;
			else if (VARATT_IS_EXTERNAL_ONDISK(PointerGetDatum(value)))
				toast_delete_datum(rel, value, is_speculative);
		}
	}
}


/* ----------
 * toast_insert_or_update -
 *
 *	Delete no-longer-used toast-entries and create new ones to
 *	make the new tuple fit on INSERT or UPDATE
 *
 * Inputs:
 *	newtup: the candidate new tuple to be inserted
 *	oldtup: the old row version for UPDATE, or NULL for INSERT
 *	options: options to be passed to heap_insert() for toast rows
 * Result:
 *	either newtup if no toasting is needed, or a palloc'd modified tuple
 *	that is what should actually get stored
 *
 * NOTE: neither newtup nor oldtup will be modified.  This is a change
 * from the pre-8.1 API of this routine.
 * ----------
 */
HeapTuple
toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
					   int options)
{
	HeapTuple	result_tuple;
	TupleDesc	tupleDesc;
	int			numAttrs;
	int			i;

	bool		need_change = false;
	bool		need_free = false;
	bool		need_delold = false;
	bool		has_nulls = false;

	Size		maxDataLen;
	Size		hoff;

	char		toast_action[MaxHeapAttributeNumber];
	bool		toast_isnull[MaxHeapAttributeNumber];
	bool		toast_oldisnull[MaxHeapAttributeNumber];
	Datum		toast_values[MaxHeapAttributeNumber];
	Datum		toast_oldvalues[MaxHeapAttributeNumber];
	struct varlena *toast_oldexternal[MaxHeapAttributeNumber];
	int32		toast_sizes[MaxHeapAttributeNumber];
	bool		toast_free[MaxHeapAttributeNumber];
	bool		toast_delold[MaxHeapAttributeNumber];

	/*
	 * Ignore the INSERT_SPECULATIVE option. Speculative insertions/super
	 * deletions just normally insert/delete the toast values. It seems
	 * easiest to deal with that here, instead on, potentially, multiple
	 * callers.
	 */
	options &= ~HEAP_INSERT_SPECULATIVE;

	/*
	 * We should only ever be called for tuples of plain relations or
	 * materialized views --- recursing on a toast rel is bad news.
	 */
	Assert(rel->rd_rel->relkind == RELKIND_RELATION ||
		   rel->rd_rel->relkind == RELKIND_MATVIEW);

	/*
	 * Get the tuple descriptor and break down the tuple(s) into fields.
	 */
	tupleDesc = rel->rd_att;
	numAttrs = tupleDesc->natts;

	Assert(numAttrs <= MaxHeapAttributeNumber);
	heap_deform_tuple(newtup, tupleDesc, toast_values, toast_isnull);
	if (oldtup != NULL)
		heap_deform_tuple(oldtup, tupleDesc, toast_oldvalues, toast_oldisnull);

	/* ----------
	 * Then collect information about the values given
	 *
	 * NOTE: toast_action[i] can have these values:
	 *		' '		default handling
	 *		'p'		already processed --- don't touch it
	 *		'x'		incompressible, but OK to move off
	 *
	 * NOTE: toast_sizes[i] is only made valid for varlena attributes with
	 *		toast_action[i] different from 'p'.
	 * ----------
	 */
	memset(toast_action, ' ', numAttrs * sizeof(char));
	memset(toast_oldexternal, 0, numAttrs * sizeof(struct varlena *));
	memset(toast_free, 0, numAttrs * sizeof(bool));
	memset(toast_delold, 0, numAttrs * sizeof(bool));

	for (i = 0; i < numAttrs; i++)
	{
		Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
		struct varlena *old_value;
		struct varlena *new_value;

		if (oldtup != NULL)
		{
			/*
			 * For UPDATE get the old and new values of this attribute
			 */
			old_value = (struct varlena *) DatumGetPointer(toast_oldvalues[i]);
			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);

			/*
			 * If the old value is stored on disk, check if it has changed so
			 * we have to delete it later.
			 */
			if (att->attlen == -1 && !toast_oldisnull[i] &&
				VARATT_IS_EXTERNAL_ONDISK(old_value))
			{
				if (toast_isnull[i] || !VARATT_IS_EXTERNAL_ONDISK(new_value) ||
					memcmp((char *) old_value, (char *) new_value,
						   VARSIZE_EXTERNAL(old_value)) != 0)
				{
					/*
					 * The old external stored value isn't needed any more
					 * after the update
					 */
					toast_delold[i] = true;
					need_delold = true;
				}
				else
				{
					/*
					 * This attribute isn't changed by this update so we reuse
					 * the original reference to the old value in the new
					 * tuple.
					 */
					toast_action[i] = 'p';
					continue;
				}
			}
		}
		else
		{
			/*
			 * For INSERT simply get the new value
			 */
			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
		}

		/*
		 * Handle NULL attributes
		 */
		if (toast_isnull[i])
		{
			toast_action[i] = 'p';
			has_nulls = true;
			continue;
		}

		/*
		 * Now look at varlena attributes
		 */
		if (att->attlen == -1)
		{
			/*
			 * If the table's attribute says PLAIN always, force it so.
			 */
			if (att->attstorage == 'p')
				toast_action[i] = 'p';

			/*
			 * We took care of UPDATE above, so any external value we find
			 * still in the tuple must be someone else's that we cannot reuse
			 * (this includes the case of an out-of-line in-memory datum).
			 * Fetch it back (without decompression, unless we are forcing
			 * PLAIN storage).  If necessary, we'll push it out as a new
			 * external value below.
			 */
			if (VARATT_IS_EXTERNAL(new_value))
			{
				toast_oldexternal[i] = new_value;
				if (att->attstorage == 'p')
					new_value = heap_tuple_untoast_attr(new_value);
				else
					new_value = heap_tuple_fetch_attr(new_value);
				toast_values[i] = PointerGetDatum(new_value);
				toast_free[i] = true;
				need_change = true;
				need_free = true;
			}

			/*
			 * Remember the size of this attribute
			 */
			toast_sizes[i] = VARSIZE_ANY(new_value);
		}
		else
		{
			/*
			 * Not a varlena attribute, plain storage always
			 */
			toast_action[i] = 'p';
		}
	}

	/* ----------
	 * Compress and/or save external until data fits into target length
	 *
	 *	1: Inline compress attributes with attstorage 'x', and store very
	 *	   large attributes with attstorage 'x' or 'e' external immediately
	 *	2: Store attributes with attstorage 'x' or 'e' external
	 *	3: Inline compress attributes with attstorage 'm'
	 *	4: Store attributes with attstorage 'm' external
	 * ----------
	 */

	/* compute header overhead --- this should match heap_form_tuple() */
	hoff = SizeofHeapTupleHeader;
	if (has_nulls)
		hoff += BITMAPLEN(numAttrs);
	hoff = MAXALIGN(hoff);
	/* now convert to a limit on the tuple data size */
	maxDataLen = RelationGetToastTupleTarget(rel, TOAST_TUPLE_TARGET) - hoff;

	/*
	 * Look for attributes with attstorage 'x' to compress.  Also find large
	 * attributes with attstorage 'x' or 'e', and store them external.
	 */
	while (heap_compute_data_size(tupleDesc,
								  toast_values, toast_isnull) > maxDataLen)
	{
		int			biggest_attno = -1;
		int32		biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
		Datum		old_value;
		Datum		new_value;

		/*
		 * Search for the biggest yet unprocessed internal attribute
		 */
		for (i = 0; i < numAttrs; i++)
		{
			Form_pg_attribute att = TupleDescAttr(tupleDesc, i);

			if (toast_action[i] != ' ')
				continue;
			if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
				continue;		/* can't happen, toast_action would be 'p' */
			if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
				continue;
			if (att->attstorage != 'x' && att->attstorage != 'e')
				continue;
			if (toast_sizes[i] > biggest_size)
			{
				biggest_attno = i;
				biggest_size = toast_sizes[i];
			}
		}

		if (biggest_attno < 0)
			break;

		/*
		 * Attempt to compress it inline, if it has attstorage 'x'
		 */
		i = biggest_attno;
		if (TupleDescAttr(tupleDesc, i)->attstorage == 'x')
		{
			old_value = toast_values[i];
			new_value = toast_compress_datum(old_value);

			if (DatumGetPointer(new_value) != NULL)
			{
				/* successful compression */
				if (toast_free[i])
					pfree(DatumGetPointer(old_value));
				toast_values[i] = new_value;
				toast_free[i] = true;
				toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
				need_change = true;
				need_free = true;
			}
			else
			{
				/* incompressible, ignore on subsequent compression passes */
				toast_action[i] = 'x';
			}
		}
		else
		{
			/* has attstorage 'e', ignore on subsequent compression passes */
			toast_action[i] = 'x';
		}

		/*
		 * If this value is by itself more than maxDataLen (after compression
		 * if any), push it out to the toast table immediately, if possible.
		 * This avoids uselessly compressing other fields in the common case
		 * where we have one long field and several short ones.
		 *
		 * XXX maybe the threshold should be less than maxDataLen?
		 */
		if (toast_sizes[i] > maxDataLen &&
			rel->rd_rel->reltoastrelid != InvalidOid)
		{
			old_value = toast_values[i];
			toast_action[i] = 'p';
			toast_values[i] = toast_save_datum(rel, toast_values[i],
											   toast_oldexternal[i], options);
			if (toast_free[i])
				pfree(DatumGetPointer(old_value));
			toast_free[i] = true;
			need_change = true;
			need_free = true;
		}
	}

	/*
	 * Second we look for attributes of attstorage 'x' or 'e' that are still
	 * inline.  But skip this if there's no toast table to push them to.
	 */
	while (heap_compute_data_size(tupleDesc,
								  toast_values, toast_isnull) > maxDataLen &&
		   rel->rd_rel->reltoastrelid != InvalidOid)
	{
		int			biggest_attno = -1;
		int32		biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
		Datum		old_value;

		/*------
		 * Search for the biggest yet inlined attribute with
		 * attstorage equals 'x' or 'e'
		 *------
		 */
		for (i = 0; i < numAttrs; i++)
		{
			Form_pg_attribute att = TupleDescAttr(tupleDesc, i);

			if (toast_action[i] == 'p')
				continue;
			if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
				continue;		/* can't happen, toast_action would be 'p' */
			if (att->attstorage != 'x' && att->attstorage != 'e')
				continue;
			if (toast_sizes[i] > biggest_size)
			{
				biggest_attno = i;
				biggest_size = toast_sizes[i];
			}
		}

		if (biggest_attno < 0)
			break;

		/*
		 * Store this external
		 */
		i = biggest_attno;
		old_value = toast_values[i];
		toast_action[i] = 'p';
		toast_values[i] = toast_save_datum(rel, toast_values[i],
										   toast_oldexternal[i], options);
		if (toast_free[i])
			pfree(DatumGetPointer(old_value));
		toast_free[i] = true;

		need_change = true;
		need_free = true;
	}

	/*
	 * Round 3 - this time we take attributes with storage 'm' into
	 * compression
	 */
	while (heap_compute_data_size(tupleDesc,
								  toast_values, toast_isnull) > maxDataLen)
	{
		int			biggest_attno = -1;
		int32		biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
		Datum		old_value;
		Datum		new_value;

		/*
		 * Search for the biggest yet uncompressed internal attribute
		 */
		for (i = 0; i < numAttrs; i++)
		{
			if (toast_action[i] != ' ')
				continue;
			if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
				continue;		/* can't happen, toast_action would be 'p' */
			if (VARATT_IS_COMPRESSED(DatumGetPointer(toast_values[i])))
				continue;
			if (TupleDescAttr(tupleDesc, i)->attstorage != 'm')
				continue;
			if (toast_sizes[i] > biggest_size)
			{
				biggest_attno = i;
				biggest_size = toast_sizes[i];
			}
		}

		if (biggest_attno < 0)
			break;

		/*
		 * Attempt to compress it inline
		 */
		i = biggest_attno;
		old_value = toast_values[i];
		new_value = toast_compress_datum(old_value);

		if (DatumGetPointer(new_value) != NULL)
		{
			/* successful compression */
			if (toast_free[i])
				pfree(DatumGetPointer(old_value));
			toast_values[i] = new_value;
			toast_free[i] = true;
			toast_sizes[i] = VARSIZE(DatumGetPointer(toast_values[i]));
			need_change = true;
			need_free = true;
		}
		else
		{
			/* incompressible, ignore on subsequent compression passes */
			toast_action[i] = 'x';
		}
	}

	/*
	 * Finally we store attributes of type 'm' externally.  At this point we
	 * increase the target tuple size, so that 'm' attributes aren't stored
	 * externally unless really necessary.
	 */
	maxDataLen = TOAST_TUPLE_TARGET_MAIN - hoff;

	while (heap_compute_data_size(tupleDesc,
								  toast_values, toast_isnull) > maxDataLen &&
		   rel->rd_rel->reltoastrelid != InvalidOid)
	{
		int			biggest_attno = -1;
		int32		biggest_size = MAXALIGN(TOAST_POINTER_SIZE);
		Datum		old_value;

		/*--------
		 * Search for the biggest yet inlined attribute with
		 * attstorage = 'm'
		 *--------
		 */
		for (i = 0; i < numAttrs; i++)
		{
			if (toast_action[i] == 'p')
				continue;
			if (VARATT_IS_EXTERNAL(DatumGetPointer(toast_values[i])))
				continue;		/* can't happen, toast_action would be 'p' */
			if (TupleDescAttr(tupleDesc, i)->attstorage != 'm')
				continue;
			if (toast_sizes[i] > biggest_size)
			{
				biggest_attno = i;
				biggest_size = toast_sizes[i];
			}
		}

		if (biggest_attno < 0)
			break;

		/*
		 * Store this external
		 */
		i = biggest_attno;
		old_value = toast_values[i];
		toast_action[i] = 'p';
		toast_values[i] = toast_save_datum(rel, toast_values[i],
										   toast_oldexternal[i], options);
		if (toast_free[i])
			pfree(DatumGetPointer(old_value));
		toast_free[i] = true;

		need_change = true;
		need_free = true;
	}

	/*
	 * In the case we toasted any values, we need to build a new heap tuple
	 * with the changed values.
	 */
	if (need_change)
	{
		HeapTupleHeader olddata = newtup->t_data;
		HeapTupleHeader new_data;
		int32		new_header_len;
		int32		new_data_len;
		int32		new_tuple_len;

		/*
		 * Calculate the new size of the tuple.
		 *
		 * Note: we used to assume here that the old tuple's t_hoff must equal
		 * the new_header_len value, but that was incorrect.  The old tuple
		 * might have a smaller-than-current natts, if there's been an ALTER
		 * TABLE ADD COLUMN since it was stored; and that would lead to a
		 * different conclusion about the size of the null bitmap, or even
		 * whether there needs to be one at all.
		 */
		new_header_len = SizeofHeapTupleHeader;
		if (has_nulls)
			new_header_len += BITMAPLEN(numAttrs);
		new_header_len = MAXALIGN(new_header_len);
		new_data_len = heap_compute_data_size(tupleDesc,
											  toast_values, toast_isnull);
		new_tuple_len = new_header_len + new_data_len;

		/*
		 * Allocate and zero the space needed, and fill HeapTupleData fields.
		 */
		result_tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + new_tuple_len);
		result_tuple->t_len = new_tuple_len;
		result_tuple->t_self = newtup->t_self;
		result_tuple->t_tableOid = newtup->t_tableOid;
		new_data = (HeapTupleHeader) ((char *) result_tuple + HEAPTUPLESIZE);
		result_tuple->t_data = new_data;

		/*
		 * Copy the existing tuple header, but adjust natts and t_hoff.
		 */
		memcpy(new_data, olddata, SizeofHeapTupleHeader);
		HeapTupleHeaderSetNatts(new_data, numAttrs);
		new_data->t_hoff = new_header_len;

		/* Copy over the data, and fill the null bitmap if needed */
		heap_fill_tuple(tupleDesc,
						toast_values,
						toast_isnull,
						(char *) new_data + new_header_len,
						new_data_len,
						&(new_data->t_infomask),
						has_nulls ? new_data->t_bits : NULL);
	}
	else
		result_tuple = newtup;

	/*
	 * Free allocated temp values
	 */
	if (need_free)
		for (i = 0; i < numAttrs; i++)
			if (toast_free[i])
				pfree(DatumGetPointer(toast_values[i]));

	/*
	 * Delete external values from the old tuple
	 */
	if (need_delold)
		for (i = 0; i < numAttrs; i++)
			if (toast_delold[i])
				toast_delete_datum(rel, toast_oldvalues[i], false);

	return result_tuple;
}


/* ----------
 * toast_flatten_tuple -
 *
 *	"Flatten" a tuple to contain no out-of-line toasted fields.
 *	(This does not eliminate compressed or short-header datums.)
 *
 *	Note: we expect the caller already checked HeapTupleHasExternal(tup),
 *	so there is no need for a short-circuit path.
 * ----------
 */
HeapTuple
toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
{
	HeapTuple	new_tuple;
	int			numAttrs = tupleDesc->natts;
	int			i;
	Datum		toast_values[MaxTupleAttributeNumber];
	bool		toast_isnull[MaxTupleAttributeNumber];
	bool		toast_free[MaxTupleAttributeNumber];

	/*
	 * Break down the tuple into fields.
	 */
	Assert(numAttrs <= MaxTupleAttributeNumber);
	heap_deform_tuple(tup, tupleDesc, toast_values, toast_isnull);

	memset(toast_free, 0, numAttrs * sizeof(bool));

	for (i = 0; i < numAttrs; i++)
	{
		/*
		 * Look at non-null varlena attributes
		 */
		if (!toast_isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
		{
			struct varlena *new_value;

			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
			if (VARATT_IS_EXTERNAL(new_value))
			{
				new_value = heap_tuple_fetch_attr(new_value);
				toast_values[i] = PointerGetDatum(new_value);
				toast_free[i] = true;
			}
		}
	}

	/*
	 * Form the reconfigured tuple.
	 */
	new_tuple = heap_form_tuple(tupleDesc, toast_values, toast_isnull);

	/*
	 * Be sure to copy the tuple's identity fields.  We also make a point of
	 * copying visibility info, just in case anybody looks at those fields in
	 * a syscache entry.
	 */
	new_tuple->t_self = tup->t_self;
	new_tuple->t_tableOid = tup->t_tableOid;

	new_tuple->t_data->t_choice = tup->t_data->t_choice;
	new_tuple->t_data->t_ctid = tup->t_data->t_ctid;
	new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
	new_tuple->t_data->t_infomask |=
		tup->t_data->t_infomask & HEAP_XACT_MASK;
	new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
	new_tuple->t_data->t_infomask2 |=
		tup->t_data->t_infomask2 & HEAP2_XACT_MASK;

	/*
	 * Free allocated temp values
	 */
	for (i = 0; i < numAttrs; i++)
		if (toast_free[i])
			pfree(DatumGetPointer(toast_values[i]));

	return new_tuple;
}


/* ----------
 * toast_flatten_tuple_to_datum -
 *
 *	"Flatten" a tuple containing out-of-line toasted fields into a Datum.
 *	The result is always palloc'd in the current memory context.
 *
 *	We have a general rule that Datums of container types (rows, arrays,
 *	ranges, etc) must not contain any external TOAST pointers.  Without
 *	this rule, we'd have to look inside each Datum when preparing a tuple
 *	for storage, which would be expensive and would fail to extend cleanly
 *	to new sorts of container types.
 *
 *	However, we don't want to say that tuples represented as HeapTuples
 *	can't contain toasted fields, so instead this routine should be called
 *	when such a HeapTuple is being converted into a Datum.
 *
 *	While we're at it, we decompress any compressed fields too.  This is not
 *	necessary for correctness, but reflects an expectation that compression
 *	will be more effective if applied to the whole tuple not individual
 *	fields.  We are not so concerned about that that we want to deconstruct
 *	and reconstruct tuples just to get rid of compressed fields, however.
 *	So callers typically won't call this unless they see that the tuple has
 *	at least one external field.
 *
 *	On the other hand, in-line short-header varlena fields are left alone.
 *	If we "untoasted" them here, they'd just get changed back to short-header
 *	format anyway within heap_fill_tuple.
 * ----------
 */
Datum
toast_flatten_tuple_to_datum(HeapTupleHeader tup,
							 uint32 tup_len,
							 TupleDesc tupleDesc)
{
	HeapTupleHeader new_data;
	int32		new_header_len;
	int32		new_data_len;
	int32		new_tuple_len;
	HeapTupleData tmptup;
	int			numAttrs = tupleDesc->natts;
	int			i;
	bool		has_nulls = false;
	Datum		toast_values[MaxTupleAttributeNumber];
	bool		toast_isnull[MaxTupleAttributeNumber];
	bool		toast_free[MaxTupleAttributeNumber];

	/* Build a temporary HeapTuple control structure */
	tmptup.t_len = tup_len;
	ItemPointerSetInvalid(&(tmptup.t_self));
	tmptup.t_tableOid = InvalidOid;
	tmptup.t_data = tup;

	/*
	 * Break down the tuple into fields.
	 */
	Assert(numAttrs <= MaxTupleAttributeNumber);
	heap_deform_tuple(&tmptup, tupleDesc, toast_values, toast_isnull);

	memset(toast_free, 0, numAttrs * sizeof(bool));

	for (i = 0; i < numAttrs; i++)
	{
		/*
		 * Look at non-null varlena attributes
		 */
		if (toast_isnull[i])
			has_nulls = true;
		else if (TupleDescAttr(tupleDesc, i)->attlen == -1)
		{
			struct varlena *new_value;

			new_value = (struct varlena *) DatumGetPointer(toast_values[i]);
			if (VARATT_IS_EXTERNAL(new_value) ||
				VARATT_IS_COMPRESSED(new_value))
			{
				new_value = heap_tuple_untoast_attr(new_value);
				toast_values[i] = PointerGetDatum(new_value);
				toast_free[i] = true;
			}
		}
	}

	/*
	 * Calculate the new size of the tuple.
	 *
	 * This should match the reconstruction code in toast_insert_or_update.
	 */
	new_header_len = SizeofHeapTupleHeader;
	if (has_nulls)
		new_header_len += BITMAPLEN(numAttrs);
	new_header_len = MAXALIGN(new_header_len);
	new_data_len = heap_compute_data_size(tupleDesc,
										  toast_values, toast_isnull);
	new_tuple_len = new_header_len + new_data_len;

	new_data = (HeapTupleHeader) palloc0(new_tuple_len);

	/*
	 * Copy the existing tuple header, but adjust natts and t_hoff.
	 */
	memcpy(new_data, tup, SizeofHeapTupleHeader);
	HeapTupleHeaderSetNatts(new_data, numAttrs);
	new_data->t_hoff = new_header_len;

	/* Set the composite-Datum header fields correctly */
	HeapTupleHeaderSetDatumLength(new_data, new_tuple_len);
	HeapTupleHeaderSetTypeId(new_data, tupleDesc->tdtypeid);
	HeapTupleHeaderSetTypMod(new_data, tupleDesc->tdtypmod);

	/* Copy over the data, and fill the null bitmap if needed */
	heap_fill_tuple(tupleDesc,
					toast_values,
					toast_isnull,
					(char *) new_data + new_header_len,
					new_data_len,
					&(new_data->t_infomask),
					has_nulls ? new_data->t_bits : NULL);

	/*
	 * Free allocated temp values
	 */
	for (i = 0; i < numAttrs; i++)
		if (toast_free[i])
			pfree(DatumGetPointer(toast_values[i]));

	return PointerGetDatum(new_data);
}


/* ----------
 * toast_build_flattened_tuple -
 *
 *	Build a tuple containing no out-of-line toasted fields.
 *	(This does not eliminate compressed or short-header datums.)
 *
 *	This is essentially just like heap_form_tuple, except that it will
 *	expand any external-data pointers beforehand.
 *
 *	It's not very clear whether it would be preferable to decompress
 *	in-line compressed datums while at it.  For now, we don't.
 * ----------
 */
HeapTuple
toast_build_flattened_tuple(TupleDesc tupleDesc,
							Datum *values,
							bool *isnull)
{
	HeapTuple	new_tuple;
	int			numAttrs = tupleDesc->natts;
	int			num_to_free;
	int			i;
	Datum		new_values[MaxTupleAttributeNumber];
	Pointer		freeable_values[MaxTupleAttributeNumber];

	/*
	 * We can pass the caller's isnull array directly to heap_form_tuple, but
	 * we potentially need to modify the values array.
	 */
	Assert(numAttrs <= MaxTupleAttributeNumber);
	memcpy(new_values, values, numAttrs * sizeof(Datum));

	num_to_free = 0;
	for (i = 0; i < numAttrs; i++)
	{
		/*
		 * Look at non-null varlena attributes
		 */
		if (!isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
		{
			struct varlena *new_value;

			new_value = (struct varlena *) DatumGetPointer(new_values[i]);
			if (VARATT_IS_EXTERNAL(new_value))
			{
				new_value = heap_tuple_fetch_attr(new_value);
				new_values[i] = PointerGetDatum(new_value);
				freeable_values[num_to_free++] = (Pointer) new_value;
			}
		}
	}

	/*
	 * Form the reconfigured tuple.
	 */
	new_tuple = heap_form_tuple(tupleDesc, new_values, isnull);

	/*
	 * Free allocated temp values
	 */
	for (i = 0; i < num_to_free; i++)
		pfree(freeable_values[i]);

	return new_tuple;
}