heaptuple.c

关系型数据库 Postgresql 6.5.2

	tp = (char *) tup + tup->t_hoff;

	/*
	 * now check for any non-fixed length attrs before our attribute
	 */
	if (!slow)
	{
		if (att[attnum]->attcacheoff != -1)
		{
			return (Datum) fetchatt(&(att[attnum]),
									tp + att[attnum]->attcacheoff);
		}
		else if (attnum == 0)
			return (Datum) fetchatt(&(att[0]), tp);
		else if (!HeapTupleAllFixed(tuple))
		{
			int			j;

			/*
			 * In for(), we make this <= and not < because we want to test
			 * if we can go past it in initializing offsets.
			 */
			for (j = 0; j <= attnum; j++)
			{
				if (att[j]->attlen < 1 && !VARLENA_FIXED_SIZE(att[j]))
				{
					slow = 1;
					break;
				}
			}
		}
	}

	/*
	 * If slow is zero, and we got here, we know that we have a tuple with
	 * no nulls or varlenas before the target attribute. If possible, we
	 * also want to initialize the remainder of the attribute cached
	 * offset values.
	 */
	if (!slow)
	{
		int			j = 1;
		long		off;

		/*
		 * need to set cache for some atts
		 */

		att[0]->attcacheoff = 0;

		while (att[j]->attcacheoff > 0)
			j++;

		if (!VARLENA_FIXED_SIZE(att[j - 1]))
			off = att[j - 1]->attcacheoff + att[j - 1]->attlen;
		else
			off = att[j - 1]->attcacheoff + att[j - 1]->atttypmod;

		for (; j <= attnum ||
		/* Can we compute more?  We will probably need them */
			 (j < tup->t_natts &&
			  att[j]->attcacheoff == -1 &&
			  (HeapTupleNoNulls(tuple) || !att_isnull(j, bp)) &&
			  (HeapTupleAllFixed(tuple) ||
			   att[j]->attlen > 0 || VARLENA_FIXED_SIZE(att[j]))); j++)
		{

			/*
			 * Fix me when going to a machine with more than a four-byte
			 * word!
			 */
			off = att_align(off, att[j]->attlen, att[j]->attalign);

			att[j]->attcacheoff = off;

			off = att_addlength(off, att[j]->attlen, tp + off);
		}

		return (Datum) fetchatt(&(att[attnum]), tp + att[attnum]->attcacheoff);
	}
	else
	{
		bool		usecache = true;
		int			off = 0;
		int			i;

		/*
		 * Now we know that we have to walk the tuple CAREFULLY.
		 *
		 * Note - This loop is a little tricky.  On iteration i we first set
		 * the offset for attribute i and figure out how much the offset
		 * should be incremented.  Finally, we need to align the offset
		 * based on the size of attribute i+1 (for which the offset has
		 * been computed). -mer 12 Dec 1991
		 */

		for (i = 0; i < attnum; i++)
		{
			if (!HeapTupleNoNulls(tuple))
			{
				if (att_isnull(i, bp))
				{
					usecache = false;
					continue;
				}
			}

			/* If we know the next offset, we can skip the rest */
			if (usecache && att[i]->attcacheoff != -1)
				off = att[i]->attcacheoff;
			else
			{
				off = att_align(off, att[i]->attlen, att[i]->attalign);

				if (usecache)
					att[i]->attcacheoff = off;
			}

			off = att_addlength(off, att[i]->attlen, tp + off);

			if (usecache &&
				att[i]->attlen == -1 && !VARLENA_FIXED_SIZE(att[i]))
				usecache = false;
		}

		off = att_align(off, att[attnum]->attlen, att[attnum]->attalign);

		return (Datum) fetchatt(&(att[attnum]), tp + off);
	}
}

/* ----------------
 *		heap_copytuple
 *
 *		returns a copy of an entire tuple
 * ----------------
 */
HeapTuple
heap_copytuple(HeapTuple tuple)
{
	HeapTuple	newTuple;

	if (!HeapTupleIsValid(tuple) || tuple->t_data == NULL)
		return NULL;

	newTuple = (HeapTuple) palloc(HEAPTUPLESIZE + tuple->t_len);
	newTuple->t_len = tuple->t_len;
	newTuple->t_self = tuple->t_self;
	newTuple->t_data = (HeapTupleHeader) ((char *) newTuple + HEAPTUPLESIZE);
	memmove((char *) newTuple->t_data,
			(char *) tuple->t_data, (int) tuple->t_len);
	return newTuple;
}

/* ----------------
 *		heap_copytuple_with_tuple
 *
 *		returns a copy of an tuple->t_data
 * ----------------
 */
void
heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
{
	if (!HeapTupleIsValid(src) || src->t_data == NULL)
	{
		dest->t_data = NULL;
		return;
	}

	dest->t_len = src->t_len;
	dest->t_self = src->t_self;
	dest->t_data = (HeapTupleHeader) palloc(src->t_len);
	memmove((char *) dest->t_data,
			(char *) src->t_data, (int) src->t_len);
	return;
}

#ifdef NOT_USED
/* ----------------
 *		heap_deformtuple
 *
 *		the inverse of heap_formtuple (see below)
 * ----------------
 */
void
heap_deformtuple(HeapTuple tuple,
				 TupleDesc tdesc,
				 Datum *values,
				 char *nulls)
{
	int			i;
	int			natts;

	Assert(HeapTupleIsValid(tuple));

	natts = tuple->t_natts;
	for (i = 0; i < natts; i++)
	{
		bool		isnull;

		values[i] = heap_getattr(tuple,
								 i + 1,
								 tdesc,
								 &isnull);
		if (isnull)
			nulls[i] = 'n';
		else
			nulls[i] = ' ';
	}
}

#endif

/* ----------------
 *		heap_formtuple
 *
 *		constructs a tuple from the given *value and *null arrays
 *
 * old comments
 *		Handles alignment by aligning 2 byte attributes on short boundries
 *		and 3 or 4 byte attributes on long word boundries on a vax; and
 *		aligning non-byte attributes on short boundries on a sun.  Does
 *		not properly align fixed length arrays of 1 or 2 byte types (yet).
 *
 *		Null attributes are indicated by a 'n' in the appropriate byte
 *		of the *null.	Non-null attributes are indicated by a ' ' (space).
 *
 *		Fix me.  (Figure that must keep context if debug--allow give oid.)
 *		Assumes in order.
 * ----------------
 */
HeapTuple
heap_formtuple(TupleDesc tupleDescriptor,
			   Datum *value,
			   char *nulls)
{
	HeapTuple	tuple;			/* return tuple */
	HeapTupleHeader td;			/* tuple data */
	int			bitmaplen;
	long		len;
	int			hoff;
	bool		hasnull = false;
	int			i;
	int			numberOfAttributes = tupleDescriptor->natts;

	len = offsetof(HeapTupleHeaderData, t_bits);

	for (i = 0; i < numberOfAttributes && !hasnull; i++)
	{
		if (nulls[i] != ' ')
			hasnull = true;
	}

	if (numberOfAttributes > MaxHeapAttributeNumber)
		elog(ERROR, "heap_formtuple: numberOfAttributes of %d > %d",
			 numberOfAttributes, MaxHeapAttributeNumber);

	if (hasnull)
	{
		bitmaplen = BITMAPLEN(numberOfAttributes);
		len += bitmaplen;
	}

	hoff = len = MAXALIGN(len);		/* be conservative here */

	len += ComputeDataSize(tupleDescriptor, value, nulls);

	tuple = (HeapTuple) palloc(HEAPTUPLESIZE + len);
	td = tuple->t_data = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);

	MemSet((char *) td, 0, (int) len);

	tuple->t_len = len;
	ItemPointerSetInvalid(&(tuple->t_self));
	td->t_natts = numberOfAttributes;
	td->t_hoff = hoff;

	DataFill((char *) td + td->t_hoff,
			 tupleDescriptor,
			 value,
			 nulls,
			 &td->t_infomask,
			 (hasnull ? td->t_bits : NULL));

	td->t_infomask |= HEAP_XMAX_INVALID;

	return tuple;
}

/* ----------------
 *		heap_modifytuple
 *
 *		forms a new tuple from an old tuple and a set of replacement values.
 *		returns a new palloc'ed tuple.
 * ----------------
 */
HeapTuple
heap_modifytuple(HeapTuple tuple,
				 Relation relation,
				 Datum *replValue,
				 char *replNull,
				 char *repl)
{
	int			attoff;
	int			numberOfAttributes;
	Datum	   *value;
	char	   *nulls;
	bool		isNull;
	HeapTuple	newTuple;
	uint8		infomask;

	/* ----------------
	 *	sanity checks
	 * ----------------
	 */
	Assert(HeapTupleIsValid(tuple));
	Assert(RelationIsValid(relation));
	Assert(PointerIsValid(replValue));
	Assert(PointerIsValid(replNull));
	Assert(PointerIsValid(repl));

	numberOfAttributes = RelationGetForm(relation)->relnatts;

	/* ----------------
	 *	allocate and fill *value and *nulls arrays from either
	 *	the tuple or the repl information, as appropriate.
	 * ----------------
	 */
	value = (Datum *) palloc(numberOfAttributes * sizeof *value);
	nulls = (char *) palloc(numberOfAttributes * sizeof *nulls);

	for (attoff = 0;
		 attoff < numberOfAttributes;
		 attoff += 1)
	{

		if (repl[attoff] == ' ')
		{
			value[attoff] = heap_getattr(tuple,
										 AttrOffsetGetAttrNumber(attoff),
										 RelationGetDescr(relation),
										 &isNull);
			nulls[attoff] = (isNull) ? 'n' : ' ';

		}
		else if (repl[attoff] != 'r')
			elog(ERROR, "heap_modifytuple: repl is \\%3d", repl[attoff]);
		else
		{						/* == 'r' */
			value[attoff] = replValue[attoff];
			nulls[attoff] = replNull[attoff];
		}
	}

	/* ----------------
	 *	create a new tuple from the *values and *nulls arrays
	 * ----------------
	 */
	newTuple = heap_formtuple(RelationGetDescr(relation),
							  value,
							  nulls);

	/* ----------------
	 *	copy the header except for t_len, t_natts, t_hoff, t_bits, t_infomask
	 * ----------------
	 */
	infomask = newTuple->t_data->t_infomask;
	memmove((char *) &newTuple->t_data->t_oid,	/* XXX */
			(char *) &tuple->t_data->t_oid,
			((char *) &tuple->t_data->t_hoff -
			 (char *) &tuple->t_data->t_oid));	/* XXX */
	newTuple->t_data->t_infomask = infomask;
	newTuple->t_data->t_natts = numberOfAttributes;
	newTuple->t_self = tuple->t_self;

	return newTuple;
}

/* ----------------------------------------------------------------
 *						other misc functions
 * ----------------------------------------------------------------
 */

HeapTuple
heap_addheader(uint32 natts,	/* max domain index */
			   int structlen,	/* its length */
			   char *structure) /* pointer to the struct */
{
	HeapTuple	tuple;
	HeapTupleHeader td;			/* tuple data */
	long		len;
	int			hoff;

	AssertArg(natts > 0);

	len = offsetof(HeapTupleHeaderData, t_bits);

	hoff = len = MAXALIGN(len);		/* be conservative */
	len += structlen;
	tuple = (HeapTuple) palloc(HEAPTUPLESIZE + len);
	td = tuple->t_data = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);

	MemSet((char *) td, 0, (int) len);

	tuple->t_len = len;
	ItemPointerSetInvalid(&(tuple->t_self));
	td->t_hoff = hoff;
	td->t_natts = natts;
	td->t_infomask = 0;
	td->t_infomask |= HEAP_XMAX_INVALID;

	memmove((char *) td + hoff, structure, structlen);

	return tuple;
}