Introduce CompactAttribute array in TupleDesc, take 2

The new compact_attrs array stores a few select fields from
FormData_pg_attribute in a more compact way, using only 16 bytes per
column instead of the 104 bytes that FormData_pg_attribute uses.  Using
CompactAttribute allows performance-critical operations such as tuple
deformation to be performed without looking at the FormData_pg_attribute
element in TupleDesc which means fewer cacheline accesses.

For some workloads, tuple deformation can be the most CPU intensive part
of processing the query.  Some testing with 16 columns on a table
where the first column is variable length showed around a 10% increase in
transactions per second for an OLAP type query performing aggregation on
the 16th column.  However, in certain cases, the increases were much
higher, up to ~25% on one AMD Zen4 machine.

This also makes pg_attribute.attcacheoff redundant.  A follow-on commit
will remove it, thus shrinking the FormData_pg_attribute struct by 4
bytes.

Author: David Rowley
Reviewed-by: Andres Freund, Victor Yegorov
Discussion: https://postgr.es/m/CAApHDvrBztXP3yx=NKNmo3xwFAFhEdyPnvrDg3=M0RhDs+4vYw@mail.gmail.com

contrib/amcheck/verify_heapam.c

@@ -1571,11 +1571,11 @@ check_tuple_attribute(HeapCheckContext *ctx)
 	struct varlena *attr;
 	char	   *tp;				/* pointer to the tuple data */
 	uint16		infomask;
-	Form_pg_attribute thisatt;
+	CompactAttribute *thisatt;
 	struct varatt_external toast_pointer;
 
 	infomask = ctx->tuphdr->t_infomask;
-	thisatt = TupleDescAttr(RelationGetDescr(ctx->rel), ctx->attnum);
+	thisatt = TupleDescCompactAttr(RelationGetDescr(ctx->rel), ctx->attnum);
 
 	tp = (char *) ctx->tuphdr + ctx->tuphdr->t_hoff;
 

contrib/pageinspect/gistfuncs.c

@@ -242,8 +242,8 @@ gist_page_items(PG_FUNCTION_ARGS)
 	}
 	else
 	{
-		tupdesc = CreateTupleDescCopy(RelationGetDescr(indexRel));
+		tupdesc = CreateTupleDescTruncatedCopy(RelationGetDescr(indexRel),
-		tupdesc->natts = IndexRelationGetNumberOfKeyAttributes(indexRel);
+											   IndexRelationGetNumberOfKeyAttributes(indexRel));
 		printflags |= RULE_INDEXDEF_KEYS_ONLY;
 	}
 

contrib/pageinspect/heapfuncs.c

@@ -334,11 +334,11 @@ tuple_data_split_internal(Oid relid, char *tupdata,
 
 	for (i = 0; i < nattrs; i++)
 	{
-		Form_pg_attribute attr;
+		CompactAttribute *attr;
 		bool		is_null;
 		bytea	   *attr_data = NULL;
 
-		attr = TupleDescAttr(tupdesc, i);
+		attr = TupleDescCompactAttr(tupdesc, i);
 
 		/*
 		 * Tuple header can specify fewer attributes than tuple descriptor as

contrib/postgres_fdw/postgres_fdw.c

@@ -1818,7 +1818,7 @@ postgresPlanForeignModify(PlannerInfo *root,
 
 		for (attnum = 1; attnum <= tupdesc->natts; attnum++)
 		{
-			Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
+			CompactAttribute *attr = TupleDescCompactAttr(tupdesc, attnum - 1);
 
 			if (!attr->attisdropped)
 				targetAttrs = lappend_int(targetAttrs, attnum);
@@ -2191,7 +2191,7 @@ postgresBeginForeignInsert(ModifyTableState *mtstate,
 	/* We transmit all columns that are defined in the foreign table. */
 	for (attnum = 1; attnum <= tupdesc->natts; attnum++)
 	{
-		Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
+		CompactAttribute *attr = TupleDescCompactAttr(tupdesc, attnum - 1);
 
 		if (!attr->attisdropped)
 			targetAttrs = lappend_int(targetAttrs, attnum);
@@ -4311,7 +4311,7 @@ convert_prep_stmt_params(PgFdwModifyState *fmstate,
 			foreach(lc, fmstate->target_attrs)
 			{
 				int			attnum = lfirst_int(lc);
-				Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);
+				CompactAttribute *attr = TupleDescCompactAttr(tupdesc, attnum - 1);
 				Datum		value;
 				bool		isnull;
 

src/backend/access/brin/brin_inclusion.c

@@ -146,12 +146,12 @@ brin_inclusion_add_value(PG_FUNCTION_ARGS)
 	Datum		result;
 	bool		new = false;
 	AttrNumber	attno;
-	Form_pg_attribute attr;
+	CompactAttribute *attr;
 
 	Assert(!isnull);
 
 	attno = column->bv_attno;
-	attr = TupleDescAttr(bdesc->bd_tupdesc, attno - 1);
+	attr = TupleDescCompactAttr(bdesc->bd_tupdesc, attno - 1);
 
 	/*
 	 * If the recorded value is null, copy the new value (which we know to be
@@ -479,7 +479,7 @@ brin_inclusion_union(PG_FUNCTION_ARGS)
 	BrinValues *col_b = (BrinValues *) PG_GETARG_POINTER(2);
 	Oid			colloid = PG_GET_COLLATION();
 	AttrNumber	attno;
-	Form_pg_attribute attr;
+	CompactAttribute *attr;
 	FmgrInfo   *finfo;
 	Datum		result;
 
@@ -487,7 +487,7 @@ brin_inclusion_union(PG_FUNCTION_ARGS)
 	Assert(!col_a->bv_allnulls && !col_b->bv_allnulls);
 
 	attno = col_a->bv_attno;
-	attr = TupleDescAttr(bdesc->bd_tupdesc, attno - 1);
+	attr = TupleDescCompactAttr(bdesc->bd_tupdesc, attno - 1);
 
 	/* If B includes empty elements, mark A similarly, if needed. */
 	if (!DatumGetBool(col_a->bv_values[INCLUSION_CONTAINS_EMPTY]) &&

src/backend/access/brin/brin_tuple.c

@@ -699,7 +699,7 @@ brin_deconstruct_tuple(BrinDesc *brdesc,
 			 datumno < brdesc->bd_info[attnum]->oi_nstored;
 			 datumno++)
 		{
-			Form_pg_attribute thisatt = TupleDescAttr(diskdsc, stored);
+			CompactAttribute *thisatt = TupleDescCompactAttr(diskdsc, stored);
 
 			if (thisatt->attlen == -1)
 			{

src/backend/access/common/attmap.c

@@ -135,7 +135,7 @@ build_attrmap_by_position(TupleDesc indesc,
 	/* Check for unused input columns */
 	for (; j < indesc->natts; j++)
 	{
-		if (TupleDescAttr(indesc, j)->attisdropped)
+		if (TupleDescCompactAttr(indesc, j)->attisdropped)
 			continue;
 		nincols++;
 		same = false;			/* we'll complain below */
@@ -299,8 +299,8 @@ check_attrmap_match(TupleDesc indesc,
 
 	for (i = 0; i < attrMap->maplen; i++)
 	{
-		Form_pg_attribute inatt = TupleDescAttr(indesc, i);
+		CompactAttribute *inatt = TupleDescCompactAttr(indesc, i);
-		Form_pg_attribute outatt = TupleDescAttr(outdesc, i);
+		CompactAttribute *outatt;
 
 		/*
 		 * If the input column has a missing attribute, we need a conversion.
@@ -311,6 +311,8 @@ check_attrmap_match(TupleDesc indesc,
 		if (attrMap->attnums[i] == (i + 1))
 			continue;
 
+		outatt = TupleDescCompactAttr(outdesc, i);
+
 		/*
 		 * If it's a dropped column and the corresponding input column is also
 		 * dropped, we don't need a conversion.  However, attlen and attalign

src/backend/access/common/heaptuple.c

@@ -83,6 +83,10 @@
 #define VARLENA_ATT_IS_PACKABLE(att) \
 	((att)->attstorage != TYPSTORAGE_PLAIN)
 
+/* FormData_pg_attribute.attstorage != TYPSTORAGE_PLAIN and an attlen of -1 */
+#define COMPACT_ATTR_IS_PACKABLE(att) \
+	((att)->attlen == -1 && (att)->attispackable)
+
 /*
  * Setup for caching pass-by-ref missing attributes in a way that survives
  * tupleDesc destruction.
@@ -147,12 +151,12 @@ Datum
 getmissingattr(TupleDesc tupleDesc,
 			   int attnum, bool *isnull)
 {
-	Form_pg_attribute att;
+	CompactAttribute *att;
 
 	Assert(attnum <= tupleDesc->natts);
 	Assert(attnum > 0);
 
-	att = TupleDescAttr(tupleDesc, attnum - 1);
+	att = TupleDescCompactAttr(tupleDesc, attnum - 1);
 
 	if (att->atthasmissing)
 	{
@@ -223,15 +227,15 @@ heap_compute_data_size(TupleDesc tupleDesc,
 	for (i = 0; i < numberOfAttributes; i++)
 	{
 		Datum		val;
-		Form_pg_attribute atti;
+		CompactAttribute *atti;
 
 		if (isnull[i])
 			continue;
 
 		val = values[i];
-		atti = TupleDescAttr(tupleDesc, i);
+		atti = TupleDescCompactAttr(tupleDesc, i);
 
-		if (ATT_IS_PACKABLE(atti) &&
+		if (COMPACT_ATTR_IS_PACKABLE(atti) &&
 			VARATT_CAN_MAKE_SHORT(DatumGetPointer(val)))
 		{
 			/*
@@ -268,7 +272,7 @@ heap_compute_data_size(TupleDesc tupleDesc,
  * Fill in either a data value or a bit in the null bitmask
  */
 static inline void
-fill_val(Form_pg_attribute att,
+fill_val(CompactAttribute *att,
 		 bits8 **bit,
 		 int *bitmask,
 		 char **dataP,
@@ -349,8 +353,7 @@ fill_val(Form_pg_attribute att,
 			data_length = VARSIZE_SHORT(val);
 			memcpy(data, val, data_length);
 		}
-		else if (VARLENA_ATT_IS_PACKABLE(att) &&
+		else if (att->attispackable && VARATT_CAN_MAKE_SHORT(val))
-				 VARATT_CAN_MAKE_SHORT(val))
 		{
 			/* convert to short varlena -- no alignment */
 			data_length = VARATT_CONVERTED_SHORT_SIZE(val);
@@ -427,7 +430,7 @@ heap_fill_tuple(TupleDesc tupleDesc,
 
 	for (i = 0; i < numberOfAttributes; i++)
 	{
-		Form_pg_attribute attr = TupleDescAttr(tupleDesc, i);
+		CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, i);
 
 		fill_val(attr,
 				 bitP ? &bitP : NULL,
@@ -461,7 +464,8 @@ heap_attisnull(HeapTuple tup, int attnum, TupleDesc tupleDesc)
 	Assert(!tupleDesc || attnum <= tupleDesc->natts);
 	if (attnum > (int) HeapTupleHeaderGetNatts(tup->t_data))
 	{
-		if (tupleDesc && TupleDescAttr(tupleDesc, attnum - 1)->atthasmissing)
+		if (tupleDesc &&
+			TupleDescCompactAttr(tupleDesc, attnum - 1)->atthasmissing)
 			return false;
 		else
 			return true;
@@ -570,13 +574,13 @@ nocachegetattr(HeapTuple tup,
 
 	if (!slow)
 	{
-		Form_pg_attribute att;
+		CompactAttribute *att;
 
 		/*
 		 * If we get here, there are no nulls up to and including the target
 		 * attribute.  If we have a cached offset, we can use it.
 		 */
-		att = TupleDescAttr(tupleDesc, attnum);
+		att = TupleDescCompactAttr(tupleDesc, attnum);
 		if (att->attcacheoff >= 0)
 			return fetchatt(att, tp + att->attcacheoff);
 
@@ -591,7 +595,7 @@ nocachegetattr(HeapTuple tup,
 
 			for (j = 0; j <= attnum; j++)
 			{
-				if (TupleDescAttr(tupleDesc, j)->attlen <= 0)
+				if (TupleDescCompactAttr(tupleDesc, j)->attlen <= 0)
 				{
 					slow = true;
 					break;
@@ -614,18 +618,18 @@ nocachegetattr(HeapTuple tup,
 		 * fixed-width columns, in hope of avoiding future visits to this
 		 * routine.
 		 */
-		TupleDescAttr(tupleDesc, 0)->attcacheoff = 0;
+		TupleDescCompactAttr(tupleDesc, 0)->attcacheoff = 0;
 
 		/* we might have set some offsets in the slow path previously */
-		while (j < natts && TupleDescAttr(tupleDesc, j)->attcacheoff > 0)
+		while (j < natts && TupleDescCompactAttr(tupleDesc, j)->attcacheoff > 0)
 			j++;
 
-		off = TupleDescAttr(tupleDesc, j - 1)->attcacheoff +
+		off = TupleDescCompactAttr(tupleDesc, j - 1)->attcacheoff +
-			TupleDescAttr(tupleDesc, j - 1)->attlen;
+			TupleDescCompactAttr(tupleDesc, j - 1)->attlen;
 
 		for (; j < natts; j++)
 		{
-			Form_pg_attribute att = TupleDescAttr(tupleDesc, j);
+			CompactAttribute *att = TupleDescCompactAttr(tupleDesc, j);
 
 			if (att->attlen <= 0)
 				break;
@@ -639,7 +643,7 @@ nocachegetattr(HeapTuple tup,
 
 		Assert(j > attnum);
 
-		off = TupleDescAttr(tupleDesc, attnum)->attcacheoff;
+		off = TupleDescCompactAttr(tupleDesc, attnum)->attcacheoff;
 	}
 	else
 	{
@@ -659,7 +663,7 @@ nocachegetattr(HeapTuple tup,
 		off = 0;
 		for (i = 0;; i++)		/* loop exit is at "break" */
 		{
-			Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
+			CompactAttribute *att = TupleDescCompactAttr(tupleDesc, i);
 
 			if (HeapTupleHasNulls(tup) && att_isnull(i, bp))
 			{
@@ -707,7 +711,7 @@ nocachegetattr(HeapTuple tup,
 		}
 	}
 
-	return fetchatt(TupleDescAttr(tupleDesc, attnum), tp + off);
+	return fetchatt(TupleDescCompactAttr(tupleDesc, attnum), tp + off);
 }
 
 /* ----------------
@@ -892,7 +896,7 @@ expand_tuple(HeapTuple *targetHeapTuple,
 		{
 			if (attrmiss[attnum].am_present)
 			{
-				Form_pg_attribute att = TupleDescAttr(tupleDesc, attnum);
+				CompactAttribute *att = TupleDescCompactAttr(tupleDesc, attnum);
 
 				targetDataLen = att_align_datum(targetDataLen,
 												att->attalign,
@@ -1020,8 +1024,7 @@ expand_tuple(HeapTuple *targetHeapTuple,
 	/* Now fill in the missing values */
 	for (attnum = sourceNatts; attnum < natts; attnum++)
 	{
-
+		CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum);
-		Form_pg_attribute attr = TupleDescAttr(tupleDesc, attnum);
 
 		if (attrmiss && attrmiss[attnum].am_present)
 		{
@@ -1370,7 +1373,7 @@ heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
 
 	for (attnum = 0; attnum < natts; attnum++)
 	{
-		Form_pg_attribute thisatt = TupleDescAttr(tupleDesc, attnum);
+		CompactAttribute *thisatt = TupleDescCompactAttr(tupleDesc, attnum);
 
 		if (hasnulls && att_isnull(attnum, bp))
 		{

src/backend/access/common/indextuple.c

@@ -303,13 +303,13 @@ nocache_index_getattr(IndexTuple tup,
 
 	if (!slow)
 	{
-		Form_pg_attribute att;
+		CompactAttribute *att;
 
 		/*
 		 * If we get here, there are no nulls up to and including the target
 		 * attribute.  If we have a cached offset, we can use it.
 		 */
-		att = TupleDescAttr(tupleDesc, attnum);
+		att = TupleDescCompactAttr(tupleDesc, attnum);
 		if (att->attcacheoff >= 0)
 			return fetchatt(att, tp + att->attcacheoff);
 
@@ -324,7 +324,7 @@ nocache_index_getattr(IndexTuple tup,
 
 			for (j = 0; j <= attnum; j++)
 			{
-				if (TupleDescAttr(tupleDesc, j)->attlen <= 0)
+				if (TupleDescCompactAttr(tupleDesc, j)->attlen <= 0)
 				{
 					slow = true;
 					break;
@@ -347,18 +347,18 @@ nocache_index_getattr(IndexTuple tup,
 		 * fixed-width columns, in hope of avoiding future visits to this
 		 * routine.
 		 */
-		TupleDescAttr(tupleDesc, 0)->attcacheoff = 0;
+		TupleDescCompactAttr(tupleDesc, 0)->attcacheoff = 0;
 
 		/* we might have set some offsets in the slow path previously */
-		while (j < natts && TupleDescAttr(tupleDesc, j)->attcacheoff > 0)
+		while (j < natts && TupleDescCompactAttr(tupleDesc, j)->attcacheoff > 0)
 			j++;
 
-		off = TupleDescAttr(tupleDesc, j - 1)->attcacheoff +
+		off = TupleDescCompactAttr(tupleDesc, j - 1)->attcacheoff +
-			TupleDescAttr(tupleDesc, j - 1)->attlen;
+			TupleDescCompactAttr(tupleDesc, j - 1)->attlen;
 
 		for (; j < natts; j++)
 		{
-			Form_pg_attribute att = TupleDescAttr(tupleDesc, j);
+			CompactAttribute *att = TupleDescCompactAttr(tupleDesc, j);
 
 			if (att->attlen <= 0)
 				break;
@@ -372,7 +372,7 @@ nocache_index_getattr(IndexTuple tup,
 
 		Assert(j > attnum);
 
-		off = TupleDescAttr(tupleDesc, attnum)->attcacheoff;
+		off = TupleDescCompactAttr(tupleDesc, attnum)->attcacheoff;
 	}
 	else
 	{
@@ -392,7 +392,7 @@ nocache_index_getattr(IndexTuple tup,
 		off = 0;
 		for (i = 0;; i++)		/* loop exit is at "break" */
 		{
-			Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
+			CompactAttribute *att = TupleDescCompactAttr(tupleDesc, i);
 
 			if (IndexTupleHasNulls(tup) && att_isnull(i, bp))
 			{
@@ -440,7 +440,7 @@ nocache_index_getattr(IndexTuple tup,
 		}
 	}
 
-	return fetchatt(TupleDescAttr(tupleDesc, attnum), tp + off);
+	return fetchatt(TupleDescCompactAttr(tupleDesc, attnum), tp + off);
 }
 
 /*
@@ -490,7 +490,7 @@ index_deform_tuple_internal(TupleDesc tupleDescriptor,
 
 	for (attnum = 0; attnum < natts; attnum++)
 	{
-		Form_pg_attribute thisatt = TupleDescAttr(tupleDescriptor, attnum);
+		CompactAttribute *thisatt = TupleDescCompactAttr(tupleDescriptor, attnum);
 
 		if (hasnulls && att_isnull(attnum, bp))
 		{
@@ -587,10 +587,8 @@ index_truncate_tuple(TupleDesc sourceDescriptor, IndexTuple source,
 	if (leavenatts == sourceDescriptor->natts)
 		return CopyIndexTuple(source);
 
-	/* Create temporary descriptor to scribble on */
+	/* Create temporary truncated tuple descriptor */
-	truncdesc = palloc(TupleDescSize(sourceDescriptor));
+	truncdesc = CreateTupleDescTruncatedCopy(sourceDescriptor, leavenatts);
-	TupleDescCopy(truncdesc, sourceDescriptor);
-	truncdesc->natts = leavenatts;
 
 	/* Deform, form copy of tuple with fewer attributes */
 	index_deform_tuple(source, truncdesc, values, isnull);

src/backend/access/common/tupdesc.c

@@ -56,6 +56,33 @@ ResourceOwnerForgetTupleDesc(ResourceOwner owner, TupleDesc tupdesc)
 	ResourceOwnerForget(owner, PointerGetDatum(tupdesc), &tupdesc_resowner_desc);
 }
 
+/*
+ * populate_compact_attribute
+ *		Fill in the corresponding CompactAttribute element from the
+ *		Form_pg_attribute for the given attribute number.  This must be called
+ *		whenever a change is made to a Form_pg_attribute in the TupleDesc.
+ */
+void
+populate_compact_attribute(TupleDesc tupdesc, int attnum)
+{
+	Form_pg_attribute src = TupleDescAttr(tupdesc, attnum);
+	CompactAttribute *dst = &tupdesc->compact_attrs[attnum];
+
+	memset(dst, 0, sizeof(CompactAttribute));
+
+	dst->attcacheoff = -1;
+	dst->attlen = src->attlen;
+
+	dst->attbyval = src->attbyval;
+	dst->attispackable = (src->attstorage != TYPSTORAGE_PLAIN);
+	dst->atthasmissing = src->atthasmissing;
+	dst->attisdropped = src->attisdropped;
+	dst->attgenerated = (src->attgenerated != '\0');
+	dst->attnotnull = src->attnotnull;
+
+	dst->attalign = src->attalign;
+}
+
 /*
  * CreateTemplateTupleDesc
  *		This function allocates an empty tuple descriptor structure.
@@ -74,18 +101,20 @@ CreateTemplateTupleDesc(int natts)
 	Assert(natts >= 0);
 
 	/*
-	 * Allocate enough memory for the tuple descriptor, including the
+	 * Allocate enough memory for the tuple descriptor, the CompactAttribute
-	 * attribute rows.
+	 * array and also an array of FormData_pg_attribute.
 	 *
-	 * Note: the attribute array stride is sizeof(FormData_pg_attribute),
+	 * Note: the FormData_pg_attribute array stride is
-	 * since we declare the array elements as FormData_pg_attribute for
+	 * sizeof(FormData_pg_attribute), since we declare the array elements as
-	 * notational convenience.  However, we only guarantee that the first
+	 * FormData_pg_attribute for notational convenience.  However, we only
-	 * ATTRIBUTE_FIXED_PART_SIZE bytes of each entry are valid; most code that
+	 * guarantee that the first ATTRIBUTE_FIXED_PART_SIZE bytes of each entry
-	 * copies tupdesc entries around copies just that much.  In principle that
+	 * are valid; most code that copies tupdesc entries around copies just
-	 * could be less due to trailing padding, although with the current
+	 * that much.  In principle that could be less due to trailing padding,
-	 * definition of pg_attribute there probably isn't any padding.
+	 * although with the current definition of pg_attribute there probably
+	 * isn't any padding.
 	 */
-	desc = (TupleDesc) palloc(offsetof(struct TupleDescData, attrs) +
+	desc = (TupleDesc) palloc(offsetof(struct TupleDescData, compact_attrs) +
+							  natts * sizeof(CompactAttribute) +
 							  natts * sizeof(FormData_pg_attribute));
 
 	/*
@@ -117,8 +146,10 @@ CreateTupleDesc(int natts, Form_pg_attribute *attrs)
 	desc = CreateTemplateTupleDesc(natts);
 
 	for (i = 0; i < natts; ++i)
+	{
 		memcpy(TupleDescAttr(desc, i), attrs[i], ATTRIBUTE_FIXED_PART_SIZE);
-
+		populate_compact_attribute(desc, i);
+	}
 	return desc;
 }
 
@@ -155,6 +186,54 @@ CreateTupleDescCopy(TupleDesc tupdesc)
 		att->atthasmissing = false;
 		att->attidentity = '\0';
 		att->attgenerated = '\0';
+
+		populate_compact_attribute(desc, i);
+	}
+
+	/* We can copy the tuple type identification, too */
+	desc->tdtypeid = tupdesc->tdtypeid;
+	desc->tdtypmod = tupdesc->tdtypmod;
+
+	return desc;
+}
+
+/*
+ * CreateTupleDescTruncatedCopy
+ *		This function creates a new TupleDesc with only the first 'natts'
+ *		attributes from an existing TupleDesc
+ *
+ * !!! Constraints and defaults are not copied !!!
+ */
+TupleDesc
+CreateTupleDescTruncatedCopy(TupleDesc tupdesc, int natts)
+{
+	TupleDesc	desc;
+	int			i;
+
+	Assert(natts <= tupdesc->natts);
+
+	desc = CreateTemplateTupleDesc(natts);
+
+	/* Flat-copy the attribute array */
+	memcpy(TupleDescAttr(desc, 0),
+		   TupleDescAttr(tupdesc, 0),
+		   desc->natts * sizeof(FormData_pg_attribute));
+
+	/*
+	 * Since we're not copying constraints and defaults, clear fields
+	 * associated with them.
+	 */
+	for (i = 0; i < desc->natts; i++)
+	{
+		Form_pg_attribute att = TupleDescAttr(desc, i);
+
+		att->attnotnull = false;
+		att->atthasdef = false;
+		att->atthasmissing = false;
+		att->attidentity = '\0';
+		att->attgenerated = '\0';
+
+		populate_compact_attribute(desc, i);
 	}
 
 	/* We can copy the tuple type identification, too */
@@ -183,6 +262,9 @@ CreateTupleDescCopyConstr(TupleDesc tupdesc)
 		   TupleDescAttr(tupdesc, 0),
 		   desc->natts * sizeof(FormData_pg_attribute));
 
+	for (i = 0; i < desc->natts; i++)
+		populate_compact_attribute(desc, i);
+
 	/* Copy the TupleConstr data structure, if any */
 	if (constr)
 	{
@@ -207,7 +289,7 @@ CreateTupleDescCopyConstr(TupleDesc tupdesc)
 			{
 				if (constr->missing[i].am_present)
 				{
-					Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+					CompactAttribute *attr = TupleDescCompactAttr(tupdesc, i);
 
 					cpy->missing[i].am_value = datumCopy(constr->missing[i].am_value,
 														 attr->attbyval,
@@ -252,7 +334,7 @@ TupleDescCopy(TupleDesc dst, TupleDesc src)
 {
 	int			i;
 
-	/* Flat-copy the header and attribute array */
+	/* Flat-copy the header and attribute arrays */
 	memcpy(dst, src, TupleDescSize(src));
 
 	/*
@@ -268,6 +350,8 @@ TupleDescCopy(TupleDesc dst, TupleDesc src)
 		att->atthasmissing = false;
 		att->attidentity = '\0';
 		att->attgenerated = '\0';
+
+		populate_compact_attribute(dst, i);
 	}
 	dst->constr = NULL;
 
@@ -322,6 +406,8 @@ TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
 	dstAtt->atthasmissing = false;
 	dstAtt->attidentity = '\0';
 	dstAtt->attgenerated = '\0';
+
+	populate_compact_attribute(dst, dstAttno - 1);
 }
 
 /*
@@ -521,7 +607,7 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
 					return false;
 				if (missval1->am_present)
 				{
-					Form_pg_attribute missatt1 = TupleDescAttr(tupdesc1, i);
+					CompactAttribute *missatt1 = TupleDescCompactAttr(tupdesc1, i);
 
 					if (!datumIsEqual(missval1->am_value, missval2->am_value,
 									  missatt1->attbyval, missatt1->attlen))
@@ -714,6 +800,8 @@ TupleDescInitEntry(TupleDesc desc,
 	att->attcompression = InvalidCompressionMethod;
 	att->attcollation = typeForm->typcollation;
 
+	populate_compact_attribute(desc, attributeNumber - 1);
+
 	ReleaseSysCache(tuple);
 }
 
@@ -821,6 +909,8 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 		default:
 			elog(ERROR, "unsupported type %u", oidtypeid);
 	}
+
+	populate_compact_attribute(desc, attributeNumber - 1);
 }
 
 /*

src/backend/access/gin/ginbulk.c

@@ -127,10 +127,10 @@ ginInitBA(BuildAccumulator *accum)
 static Datum
 getDatumCopy(BuildAccumulator *accum, OffsetNumber attnum, Datum value)
 {
-	Form_pg_attribute att;
+	CompactAttribute *att;
 	Datum		res;
 
-	att = TupleDescAttr(accum->ginstate->origTupdesc, attnum - 1);
+	att = TupleDescCompactAttr(accum->ginstate->origTupdesc, attnum - 1);
 	if (att->attbyval)
 		res = value;
 	else

src/backend/access/gin/ginget.c

@@ -122,7 +122,7 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
 				   GinScanEntry scanEntry, Snapshot snapshot)
 {
 	OffsetNumber attnum;
-	Form_pg_attribute attr;
+	CompactAttribute *attr;
 
 	/* Initialize empty bitmap result */
 	scanEntry->matchBitmap = tbm_create(work_mem * 1024L, NULL);
@@ -134,7 +134,7 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
 
 	/* Locate tupdesc entry for key column (for attbyval/attlen data) */
 	attnum = scanEntry->attnum;
-	attr = TupleDescAttr(btree->ginstate->origTupdesc, attnum - 1);
+	attr = TupleDescCompactAttr(btree->ginstate->origTupdesc, attnum - 1);
 
 	/*
 	 * Predicate lock entry leaf page, following pages will be locked by

src/backend/access/gist/gist.c

@@ -1557,9 +1557,8 @@ initGISTstate(Relation index)
 	 * tuples during page split.  Also, B-tree is not adjusting tuples on
 	 * internal pages the way GiST does.
 	 */
-	giststate->nonLeafTupdesc = CreateTupleDescCopyConstr(index->rd_att);
+	giststate->nonLeafTupdesc = CreateTupleDescTruncatedCopy(index->rd_att,
-	giststate->nonLeafTupdesc->natts =
+															 IndexRelationGetNumberOfKeyAttributes(index));
-		IndexRelationGetNumberOfKeyAttributes(index);
 
 	for (i = 0; i < IndexRelationGetNumberOfKeyAttributes(index); i++)
 	{

src/backend/access/gist/gistbuild.c

@@ -657,10 +657,12 @@ gistInitBuffering(GISTBuildState *buildstate)
 	itupMinSize = (Size) MAXALIGN(sizeof(IndexTupleData));
 	for (i = 0; i < index->rd_att->natts; i++)
 	{
-		if (TupleDescAttr(index->rd_att, i)->attlen < 0)
+		CompactAttribute *attr = TupleDescCompactAttr(index->rd_att, i);
+
+		if (attr->attlen < 0)
 			itupMinSize += VARHDRSZ;
 		else
-			itupMinSize += TupleDescAttr(index->rd_att, i)->attlen;
+			itupMinSize += attr->attlen;
 	}
 
 	/* Calculate average and maximal number of index tuples which fit to page */

src/backend/access/heap/heapam.c

@@ -4200,8 +4200,6 @@ static bool
 heap_attr_equals(TupleDesc tupdesc, int attrnum, Datum value1, Datum value2,
 				 bool isnull1, bool isnull2)
 {
-	Form_pg_attribute att;
-
 	/*
 	 * If one value is NULL and other is not, then they are certainly not
 	 * equal
@@ -4231,8 +4229,10 @@ heap_attr_equals(TupleDesc tupdesc, int attrnum, Datum value1, Datum value2,
 	}
 	else
 	{
+		CompactAttribute *att;
+
 		Assert(attrnum <= tupdesc->natts);
-		att = TupleDescAttr(tupdesc, attrnum - 1);
+		att = TupleDescCompactAttr(tupdesc, attrnum - 1);
 		return datumIsEqual(value1, value2, att->attbyval, att->attlen);
 	}
 }
@@ -4314,7 +4314,7 @@ HeapDetermineColumnsInfo(Relation relation,
 		 * that system attributes can't be stored externally.
 		 */
 		if (attrnum < 0 || isnull1 ||
-			TupleDescAttr(tupdesc, attrnum - 1)->attlen != -1)
+			TupleDescCompactAttr(tupdesc, attrnum - 1)->attlen != -1)
 			continue;
 
 		/*

src/backend/access/heap/heapam_handler.c

@@ -2550,7 +2550,7 @@ reform_and_rewrite_tuple(HeapTuple tuple,
 	/* Be sure to null out any dropped columns */
 	for (i = 0; i < newTupDesc->natts; i++)
 	{
-		if (TupleDescAttr(newTupDesc, i)->attisdropped)
+		if (TupleDescCompactAttr(newTupDesc, i)->attisdropped)
 			isnull[i] = true;
 	}
 

src/backend/access/heap/heaptoast.c

@@ -369,7 +369,7 @@ toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc)
 		/*
 		 * Look at non-null varlena attributes
 		 */
-		if (!toast_isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
+		if (!toast_isnull[i] && TupleDescCompactAttr(tupleDesc, i)->attlen == -1)
 		{
 			struct varlena *new_value;
 
@@ -483,7 +483,7 @@ toast_flatten_tuple_to_datum(HeapTupleHeader tup,
 		 */
 		if (toast_isnull[i])
 			has_nulls = true;
-		else if (TupleDescAttr(tupleDesc, i)->attlen == -1)
+		else if (TupleDescCompactAttr(tupleDesc, i)->attlen == -1)
 		{
 			struct varlena *new_value;
 
@@ -584,7 +584,7 @@ toast_build_flattened_tuple(TupleDesc tupleDesc,
 		/*
 		 * Look at non-null varlena attributes
 		 */
-		if (!isnull[i] && TupleDescAttr(tupleDesc, i)->attlen == -1)
+		if (!isnull[i] && TupleDescCompactAttr(tupleDesc, i)->attlen == -1)
 		{
 			struct varlena *new_value;
 

src/backend/access/nbtree/nbtutils.c

@@ -4890,11 +4890,11 @@ _bt_keep_natts_fast(Relation rel, IndexTuple lastleft, IndexTuple firstright)
 					datum2;
 		bool		isNull1,
 					isNull2;
-		Form_pg_attribute att;
+		CompactAttribute *att;
 
 		datum1 = index_getattr(lastleft, attnum, itupdesc, &isNull1);
 		datum2 = index_getattr(firstright, attnum, itupdesc, &isNull2);
-		att = TupleDescAttr(itupdesc, attnum - 1);
+		att = TupleDescCompactAttr(itupdesc, attnum - 1);
 
 		if (isNull1 != isNull2)
 			break;

src/backend/access/spgist/spgdoinsert.c

@@ -1974,7 +1974,7 @@ spgdoinsert(Relation index, SpGistState *state,
 	{
 		if (!isnulls[i])
 		{
-			if (TupleDescAttr(leafDescriptor, i)->attlen == -1)
+			if (TupleDescCompactAttr(leafDescriptor, i)->attlen == -1)
 				leafDatums[i] = PointerGetDatum(PG_DETOAST_DATUM(datums[i]));
 			else
 				leafDatums[i] = datums[i];

src/backend/access/spgist/spgutils.c

@@ -331,7 +331,9 @@ getSpGistTupleDesc(Relation index, SpGistTypeDesc *keyType)
 		att->attcollation = InvalidOid;
 		/* In case we changed typlen, we'd better reset following offsets */
 		for (int i = spgFirstIncludeColumn; i < outTupDesc->natts; i++)
-			TupleDescAttr(outTupDesc, i)->attcacheoff = -1;
+			TupleDescCompactAttr(outTupDesc, i)->attcacheoff = -1;
+
+		populate_compact_attribute(outTupDesc, spgKeyColumn);
 	}
 	return outTupDesc;
 }

src/backend/access/table/toast_helper.c

@@ -324,7 +324,7 @@ toast_delete_external(Relation rel, const Datum *values, const bool *isnull,
 
 	for (i = 0; i < numAttrs; i++)
 	{
-		if (TupleDescAttr(tupleDesc, i)->attlen == -1)
+		if (TupleDescCompactAttr(tupleDesc, i)->attlen == -1)
 		{
 			Datum		value = values[i];
 

src/backend/catalog/index.c

@@ -477,6 +477,8 @@ ConstructTupleDescriptor(Relation heapRelation,
 
 			ReleaseSysCache(tuple);
 		}
+
+		populate_compact_attribute(indexTupDesc, i);
 	}
 
 	pfree(amroutine);

src/backend/commands/copy.c

@@ -954,9 +954,9 @@ CopyGetAttnums(TupleDesc tupDesc, Relation rel, List *attnamelist)
 
 		for (i = 0; i < attr_count; i++)
 		{
-			if (TupleDescAttr(tupDesc, i)->attisdropped)
+			CompactAttribute *attr = TupleDescCompactAttr(tupDesc, i);
-				continue;
+
-			if (TupleDescAttr(tupDesc, i)->attgenerated)
+			if (attr->attisdropped || attr->attgenerated)
 				continue;
 			attnums = lappend_int(attnums, i + 1);
 		}

src/backend/commands/tablecmds.c

@@ -980,6 +980,8 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 			cookedDefaults = lappend(cookedDefaults, cooked);
 			attr->atthasdef = true;
 		}
+
+		populate_compact_attribute(descriptor, attnum - 1);
 	}
 
 	/*
@@ -1396,6 +1398,8 @@ BuildDescForRelation(const List *columns)
 			att->attstorage = entry->storage;
 		else if (entry->storage_name)
 			att->attstorage = GetAttributeStorage(att->atttypid, entry->storage_name);
+
+		populate_compact_attribute(desc, attnum - 1);
 	}
 
 	return desc;

src/backend/executor/execExpr.c

@@ -598,7 +598,7 @@ ExecBuildUpdateProjection(List *targetList,
 	 */
 	for (int attnum = relDesc->natts; attnum > 0; attnum--)
 	{
-		Form_pg_attribute attr = TupleDescAttr(relDesc, attnum - 1);
+		CompactAttribute *attr = TupleDescCompactAttr(relDesc, attnum - 1);
 
 		if (attr->attisdropped)
 			continue;
@@ -694,7 +694,7 @@ ExecBuildUpdateProjection(List *targetList,
 	 */
 	for (int attnum = 1; attnum <= relDesc->natts; attnum++)
 	{
-		Form_pg_attribute attr = TupleDescAttr(relDesc, attnum - 1);
+		CompactAttribute *attr = TupleDescCompactAttr(relDesc, attnum - 1);
 
 		if (attr->attisdropped)
 		{

src/backend/executor/execExprInterp.c

@@ -3152,7 +3152,7 @@ ExecEvalRowNullInt(ExprState *state, ExprEvalStep *op,
 	for (int att = 1; att <= tupDesc->natts; att++)
 	{
 		/* ignore dropped columns */
-		if (TupleDescAttr(tupDesc, att - 1)->attisdropped)
+		if (TupleDescCompactAttr(tupDesc, att - 1)->attisdropped)
 			continue;
 		if (heap_attisnull(&tmptup, att, tupDesc))
 		{
@@ -5296,8 +5296,8 @@ ExecEvalWholeRowVar(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
 
 		for (int i = 0; i < var_tupdesc->natts; i++)
 		{
-			Form_pg_attribute vattr = TupleDescAttr(var_tupdesc, i);
+			CompactAttribute *vattr = TupleDescCompactAttr(var_tupdesc, i);
-			Form_pg_attribute sattr = TupleDescAttr(tupleDesc, i);
+			CompactAttribute *sattr = TupleDescCompactAttr(tupleDesc, i);
 
 			if (!vattr->attisdropped)
 				continue;		/* already checked non-dropped cols */

src/backend/executor/execJunk.c

@@ -169,7 +169,7 @@ ExecInitJunkFilterConversion(List *targetList,
 		t = list_head(targetList);
 		for (i = 0; i < cleanLength; i++)
 		{
-			if (TupleDescAttr(cleanTupType, i)->attisdropped)
+			if (TupleDescCompactAttr(cleanTupType, i)->attisdropped)
 				continue;		/* map entry is already zero */
 			for (;;)
 			{

src/backend/executor/execTuples.c

@@ -187,7 +187,7 @@ tts_virtual_materialize(TupleTableSlot *slot)
 	/* compute size of memory required */
 	for (int natt = 0; natt < desc->natts; natt++)
 	{
-		Form_pg_attribute att = TupleDescAttr(desc, natt);
+		CompactAttribute *att = TupleDescCompactAttr(desc, natt);
 		Datum		val;
 
 		if (att->attbyval || slot->tts_isnull[natt])
@@ -223,7 +223,7 @@ tts_virtual_materialize(TupleTableSlot *slot)
 	/* and copy all attributes into the pre-allocated space */
 	for (int natt = 0; natt < desc->natts; natt++)
 	{
-		Form_pg_attribute att = TupleDescAttr(desc, natt);
+		CompactAttribute *att = TupleDescCompactAttr(desc, natt);
 		Datum		val;
 
 		if (att->attbyval || slot->tts_isnull[natt])
@@ -1044,7 +1044,7 @@ slot_deform_heap_tuple(TupleTableSlot *slot, HeapTuple tuple, uint32 *offp,
 
 	for (; attnum < natts; attnum++)
 	{
-		Form_pg_attribute thisatt = TupleDescAttr(tupleDesc, attnum);
+		CompactAttribute *thisatt = TupleDescCompactAttr(tupleDesc, attnum);
 
 		if (hasnulls && att_isnull(attnum, bp))
 		{
@@ -2237,7 +2237,7 @@ BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
 	 */
 	for (i = 0; i < natts; i++)
 	{
-		if (!TupleDescAttr(tupdesc, i)->attisdropped)
+		if (!TupleDescCompactAttr(tupdesc, i)->attisdropped)
 		{
 			/* Non-dropped attributes */
 			dvalues[i] = InputFunctionCall(&attinmeta->attinfuncs[i],

src/backend/executor/functions.c

@@ -1886,7 +1886,7 @@ check_sql_fn_retval(List *queryTreeLists,
 		/* remaining columns in rettupdesc had better all be dropped */
 		for (colindex++; colindex <= tupnatts; colindex++)
 		{
-			if (!TupleDescAttr(rettupdesc, colindex - 1)->attisdropped)
+			if (!TupleDescCompactAttr(rettupdesc, colindex - 1)->attisdropped)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
 						 errmsg("return type mismatch in function declared to return %s",

src/backend/executor/nodeMemoize.c

@@ -175,10 +175,10 @@ MemoizeHash_hash(struct memoize_hash *tb, const MemoizeKey *key)
 
 			if (!pslot->tts_isnull[i])	/* treat nulls as having hash key 0 */
 			{
-				Form_pg_attribute attr;
+				CompactAttribute *attr;
 				uint32		hkey;
 
-				attr = TupleDescAttr(pslot->tts_tupleDescriptor, i);
+				attr = TupleDescCompactAttr(pslot->tts_tupleDescriptor, i);
 
 				hkey = datum_image_hash(pslot->tts_values[i], attr->attbyval, attr->attlen);
 
@@ -242,7 +242,7 @@ MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
 
 		for (int i = 0; i < numkeys; i++)
 		{
-			Form_pg_attribute attr;
+			CompactAttribute *attr;
 
 			if (tslot->tts_isnull[i] != pslot->tts_isnull[i])
 			{
@@ -255,7 +255,7 @@ MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
 				continue;
 
 			/* perform binary comparison on the two datums */
-			attr = TupleDescAttr(tslot->tts_tupleDescriptor, i);
+			attr = TupleDescCompactAttr(tslot->tts_tupleDescriptor, i);
 			if (!datum_image_eq(tslot->tts_values[i], pslot->tts_values[i],
 								attr->attbyval, attr->attlen))
 			{

src/backend/executor/nodeModifyTable.c

@@ -496,14 +496,14 @@ ExecComputeStoredGenerated(ResultRelInfo *resultRelInfo,
 
 	for (int i = 0; i < natts; i++)
 	{
-		Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+		CompactAttribute *attr = TupleDescCompactAttr(tupdesc, i);
 
 		if (ri_GeneratedExprs[i])
 		{
 			Datum		val;
 			bool		isnull;
 
-			Assert(attr->attgenerated == ATTRIBUTE_GENERATED_STORED);
+			Assert(TupleDescAttr(tupdesc, i)->attgenerated == ATTRIBUTE_GENERATED_STORED);
 
 			econtext->ecxt_scantuple = slot;
 

src/backend/executor/nodeValuesscan.c

@@ -142,8 +142,8 @@ ValuesNext(ValuesScanState *node)
 		foreach(lc, exprstatelist)
 		{
 			ExprState  *estate = (ExprState *) lfirst(lc);
-			Form_pg_attribute attr = TupleDescAttr(slot->tts_tupleDescriptor,
+			CompactAttribute *attr = TupleDescCompactAttr(slot->tts_tupleDescriptor,
-												   resind);
+														  resind);
 
 			values[resind] = ExecEvalExpr(estate,
 										  econtext,

src/backend/executor/tstoreReceiver.c

@@ -65,7 +65,7 @@ tstoreStartupReceiver(DestReceiver *self, int operation, TupleDesc typeinfo)
 	{
 		for (i = 0; i < natts; i++)
 		{
-			Form_pg_attribute attr = TupleDescAttr(typeinfo, i);
+			CompactAttribute *attr = TupleDescCompactAttr(typeinfo, i);
 
 			if (attr->attisdropped)
 				continue;
@@ -154,7 +154,7 @@ tstoreReceiveSlot_detoast(TupleTableSlot *slot, DestReceiver *self)
 	for (i = 0; i < natts; i++)
 	{
 		Datum		val = slot->tts_values[i];
-		Form_pg_attribute attr = TupleDescAttr(typeinfo, i);
+		CompactAttribute *attr = TupleDescCompactAttr(typeinfo, i);
 
 		if (!attr->attisdropped && attr->attlen == -1 && !slot->tts_isnull[i])
 		{

src/backend/jit/llvm/llvmjit_deform.c

@@ -110,7 +110,7 @@ slot_compile_deform(LLVMJitContext *context, TupleDesc desc,
 	 */
 	for (attnum = 0; attnum < desc->natts; attnum++)
 	{
-		Form_pg_attribute att = TupleDescAttr(desc, attnum);
+		CompactAttribute *att = TupleDescCompactAttr(desc, attnum);
 
 		/*
 		 * If the column is declared NOT NULL then it must be present in every
@@ -393,7 +393,7 @@ slot_compile_deform(LLVMJitContext *context, TupleDesc desc,
 	 */
 	for (attnum = 0; attnum < natts; attnum++)
 	{
-		Form_pg_attribute att = TupleDescAttr(desc, attnum);
+		CompactAttribute *att = TupleDescCompactAttr(desc, attnum);
 		LLVMValueRef v_incby;
 		int			alignto;
 		LLVMValueRef l_attno = l_int16_const(lc, attnum);

src/backend/optimizer/util/plancat.c

@@ -175,12 +175,12 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	{
 		for (int i = 0; i < relation->rd_att->natts; i++)
 		{
-			Form_pg_attribute attr = TupleDescAttr(relation->rd_att, i);
+			CompactAttribute *attr = TupleDescCompactAttr(relation->rd_att, i);
 
 			if (attr->attnotnull)
 			{
 				rel->notnullattnums = bms_add_member(rel->notnullattnums,
-													 attr->attnum);
+													 i + 1);
 
 				/*
 				 * Per RemoveAttributeById(), dropped columns will have their

src/backend/replication/pgoutput/pgoutput.c

@@ -1344,7 +1344,7 @@ pgoutput_row_filter(Relation relation, TupleTableSlot *old_slot,
 	 */
 	for (i = 0; i < desc->natts; i++)
 	{
-		Form_pg_attribute att = TupleDescAttr(desc, i);
+		CompactAttribute *att = TupleDescCompactAttr(desc, i);
 
 		/*
 		 * if the column in the new tuple or old tuple is null, nothing to do

src/backend/utils/adt/expandedrecord.c

@@ -699,7 +699,7 @@ ER_get_flat_size(ExpandedObjectHeader *eohptr)
 	{
 		for (i = 0; i < erh->nfields; i++)
 		{
-			Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+			CompactAttribute *attr = TupleDescCompactAttr(tupdesc, i);
 
 			if (!erh->dnulls[i] &&
 				!attr->attbyval && attr->attlen == -1 &&
@@ -1115,7 +1115,7 @@ expanded_record_set_field_internal(ExpandedRecordHeader *erh, int fnumber,
 								   bool check_constraints)
 {
 	TupleDesc	tupdesc;
-	Form_pg_attribute attr;
+	CompactAttribute *attr;
 	Datum	   *dvalues;
 	bool	   *dnulls;
 	char	   *oldValue;
@@ -1146,7 +1146,7 @@ expanded_record_set_field_internal(ExpandedRecordHeader *erh, int fnumber,
 	 * Copy new field value into record's context, and deal with detoasting,
 	 * if needed.
 	 */
-	attr = TupleDescAttr(tupdesc, fnumber - 1);
+	attr = TupleDescCompactAttr(tupdesc, fnumber - 1);
 	if (!isnull && !attr->attbyval)
 	{
 		MemoryContext oldcxt;
@@ -1279,7 +1279,7 @@ expanded_record_set_fields(ExpandedRecordHeader *erh,
 
 	for (fnumber = 0; fnumber < erh->nfields; fnumber++)
 	{
-		Form_pg_attribute attr = TupleDescAttr(tupdesc, fnumber);
+		CompactAttribute *attr = TupleDescCompactAttr(tupdesc, fnumber);
 		Datum		newValue;
 		bool		isnull;
 
@@ -1541,7 +1541,7 @@ check_domain_for_new_field(ExpandedRecordHeader *erh, int fnumber,
 	 */
 	if (!isnull)
 	{
-		Form_pg_attribute attr = TupleDescAttr(erh->er_tupdesc, fnumber - 1);
+		CompactAttribute *attr = TupleDescCompactAttr(erh->er_tupdesc, fnumber - 1);
 
 		if (!attr->attbyval && attr->attlen == -1 &&
 			VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))

src/backend/utils/adt/ri_triggers.c

@@ -2932,7 +2932,7 @@ ri_KeysEqual(Relation rel, TupleTableSlot *oldslot, TupleTableSlot *newslot,
 			 * difference for ON UPDATE CASCADE, but for consistency we treat
 			 * all changes to the PK the same.
 			 */
-			Form_pg_attribute att = TupleDescAttr(oldslot->tts_tupleDescriptor, attnums[i] - 1);
+			CompactAttribute *att = TupleDescCompactAttr(oldslot->tts_tupleDescriptor, attnums[i] - 1);
 
 			if (!datum_image_eq(oldvalue, newvalue, att->attbyval, att->attlen))
 				return false;

src/backend/utils/cache/relcache.c

@@ -585,6 +585,8 @@ RelationBuildTupleDesc(Relation relation)
 			   attp,
 			   ATTRIBUTE_FIXED_PART_SIZE);
 
+		populate_compact_attribute(relation->rd_att, attnum - 1);
+
 		/* Update constraint/default info */
 		if (attp->attnotnull)
 			constr->has_not_null = true;
@@ -661,8 +663,7 @@ RelationBuildTupleDesc(Relation relation)
 
 	/*
 	 * The attcacheoff values we read from pg_attribute should all be -1
-	 * ("unknown").  Verify this if assert checking is on.  They will be
+	 * ("unknown").  Verify this if assert checking is on.
-	 * computed when and if needed during tuple access.
 	 */
 #ifdef USE_ASSERT_CHECKING
 	{
@@ -674,12 +675,12 @@ RelationBuildTupleDesc(Relation relation)
 #endif
 
 	/*
-	 * However, we can easily set the attcacheoff value for the first
+	 * We can easily set the attcacheoff value for the first attribute: it
-	 * attribute: it must be zero.  This eliminates the need for special cases
+	 * must be zero.  This eliminates the need for special cases for attnum=1
-	 * for attnum=1 that used to exist in fastgetattr() and index_getattr().
+	 * that used to exist in fastgetattr() and index_getattr().
 	 */
 	if (RelationGetNumberOfAttributes(relation) > 0)
-		TupleDescAttr(relation->rd_att, 0)->attcacheoff = 0;
+		TupleDescCompactAttr(relation->rd_att, 0)->attcacheoff = 0;
 
 	/*
 	 * Set up constraint/default info
@@ -1965,10 +1966,12 @@ formrdesc(const char *relationName, Oid relationReltype,
 		has_not_null |= attrs[i].attnotnull;
 		/* make sure attcacheoff is valid */
 		TupleDescAttr(relation->rd_att, i)->attcacheoff = -1;
+
+		populate_compact_attribute(relation->rd_att, i);
 	}
 
 	/* initialize first attribute's attcacheoff, cf RelationBuildTupleDesc */
-	TupleDescAttr(relation->rd_att, 0)->attcacheoff = 0;
+	TupleDescCompactAttr(relation->rd_att, 0)->attcacheoff = 0;
 
 	/* mark not-null status */
 	if (has_not_null)
@@ -3579,6 +3582,7 @@ RelationBuildLocalRelation(const char *relname,
 		datt->attgenerated = satt->attgenerated;
 		datt->attnotnull = satt->attnotnull;
 		has_not_null |= satt->attnotnull;
+		populate_compact_attribute(rel->rd_att, i);
 	}
 
 	if (has_not_null)
@@ -4399,10 +4403,12 @@ BuildHardcodedDescriptor(int natts, const FormData_pg_attribute *attrs)
 		memcpy(TupleDescAttr(result, i), &attrs[i], ATTRIBUTE_FIXED_PART_SIZE);
 		/* make sure attcacheoff is valid */
 		TupleDescAttr(result, i)->attcacheoff = -1;
+
+		populate_compact_attribute(result, i);
 	}
 
 	/* initialize first attribute's attcacheoff, cf RelationBuildTupleDesc */
-	TupleDescAttr(result, 0)->attcacheoff = 0;
+	TupleDescCompactAttr(result, 0)->attcacheoff = 0;
 
 	/* Note: we don't bother to set up a TupleConstr entry */
 
@@ -6199,6 +6205,8 @@ load_relcache_init_file(bool shared)
 				goto read_failed;
 
 			has_not_null |= attr->attnotnull;
+
+			populate_compact_attribute(rel->rd_att, i);
 		}
 
 		/* next read the access method specific field */

src/include/access/htup_details.h

@@ -758,9 +758,9 @@ fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
 	*isnull = false;
 	if (HeapTupleNoNulls(tup))
 	{
-		Form_pg_attribute att;
+		CompactAttribute *att;
 
-		att = TupleDescAttr(tupleDesc, attnum - 1);
+		att = TupleDescCompactAttr(tupleDesc, attnum - 1);
 		if (att->attcacheoff >= 0)
 			return fetchatt(att, (char *) tup->t_data + tup->t_data->t_hoff +
 							att->attcacheoff);

src/include/access/itup.h

@@ -124,11 +124,13 @@ index_getattr(IndexTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
 
 	if (!IndexTupleHasNulls(tup))
 	{
-		if (TupleDescAttr(tupleDesc, attnum - 1)->attcacheoff >= 0)
+		CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum - 1);
+
+		if (attr->attcacheoff >= 0)
 		{
-			return fetchatt(TupleDescAttr(tupleDesc, attnum - 1),
+			return fetchatt(attr,
-							(char *) tup + IndexInfoFindDataOffset(tup->t_info)
+							(char *) tup + IndexInfoFindDataOffset(tup->t_info) +
-							+ TupleDescAttr(tupleDesc, attnum - 1)->attcacheoff);
+							attr->attcacheoff);
 		}
 		else
 			return nocache_index_getattr(tup, attnum, tupleDesc);

src/include/access/tupdesc.h

@@ -45,6 +45,39 @@ typedef struct TupleConstr
 	bool		has_generated_stored;
 } TupleConstr;
 
+/*
+ * CompactAttribute
+ *		Cut-down version of FormData_pg_attribute for faster access for tasks
+ *		such as tuple deformation.  The fields of this struct are populated
+ *		using the populate_compact_attribute() function, which must be called
+ *		directly after the FormData_pg_attribute struct is populated or
+ *		altered in any way.
+ *
+ * Currently, this struct is 16 bytes.  Any code changes which enlarge this
+ * struct should be considered very carefully.
+ *
+ * Code which must access a TupleDesc's attribute data should always make use
+ * the fields of this struct when required fields are available here.  It's
+ * more efficient to access the memory in CompactAttribute due to it being a
+ * more compact representation of FormData_pg_attribute and also because
+ * accessing the FormData_pg_attribute requires an additional calculations to
+ * obtain the base address of the array within the TupleDesc.
+ */
+typedef struct CompactAttribute
+{
+	int32		attcacheoff;	/* fixed offset into tuple, if known, or -1 */
+	int16		attlen;			/* attr len in bytes or -1 = varlen, -2 =
+								 * cstring */
+	bool		attbyval;		/* as FormData_pg_attribute.attbyval */
+	bool		attispackable;	/* FormData_pg_attribute.attstorage !=
+								 * TYPSTORAGE_PLAIN */
+	bool		atthasmissing;	/* as FormData_pg_attribute.atthasmissing */
+	bool		attisdropped;	/* as FormData_pg_attribute.attisdropped */
+	bool		attgenerated;	/* FormData_pg_attribute.attgenerated != '\0' */
+	bool		attnotnull;		/* as FormData_pg_attribute.attnotnull */
+	char		attalign;		/* alignment requirement */
+} CompactAttribute;
+
 /*
  * This struct is passed around within the backend to describe the structure
  * of tuples.  For tuples coming from on-disk relations, the information is
@@ -75,6 +108,21 @@ typedef struct TupleConstr
  * context and go away when the context is freed.  We set the tdrefcount
  * field of such a descriptor to -1, while reference-counted descriptors
  * always have tdrefcount >= 0.
+ *
+ * Beyond the compact_attrs variable length array, the TupleDesc stores an
+ * array of FormData_pg_attribute.  The TupleDescAttr() function, as defined
+ * below, takes care of calculating the address of the elements of the
+ * FormData_pg_attribute array.
+ *
+ * The array of CompactAttribute is effectively an abbreviated version of the
+ * array of FormData_pg_attribute.  Because CompactAttribute is significantly
+ * smaller than FormData_pg_attribute, code, especially performance-critical
+ * code, should prioritize using the fields from the CompactAttribute over the
+ * equivalent fields in FormData_pg_attribute.
+ *
+ * Any code making changes manually to and fields in the FormData_pg_attribute
+ * array must subsequently call populate_compact_attribute() to flush the
+ * changes out to the corresponding 'compact_attrs' element.
  */
 typedef struct TupleDescData
 {
@@ -83,13 +131,68 @@ typedef struct TupleDescData
 	int32		tdtypmod;		/* typmod for tuple type */
 	int			tdrefcount;		/* reference count, or -1 if not counting */
 	TupleConstr *constr;		/* constraints, or NULL if none */
-	/* attrs[N] is the description of Attribute Number N+1 */
+	/* compact_attrs[N] is the compact metadata of Attribute Number N+1 */
-	FormData_pg_attribute attrs[FLEXIBLE_ARRAY_MEMBER];
+	CompactAttribute compact_attrs[FLEXIBLE_ARRAY_MEMBER];
 }			TupleDescData;
 typedef struct TupleDescData *TupleDesc;
 
-/* Accessor for the i'th attribute of tupdesc. */
+extern void populate_compact_attribute(TupleDesc tupdesc, int attnum);
-#define TupleDescAttr(tupdesc, i) (&(tupdesc)->attrs[(i)])
+
+/*
+ * Calculates the base address of the Form_pg_attribute at the end of the
+ * TupleDescData struct.
+ */
+#define TupleDescAttrAddress(desc) \
+	(Form_pg_attribute) ((char *) (desc) + \
+	 (offsetof(struct TupleDescData, compact_attrs) + \
+	 (desc)->natts * sizeof(CompactAttribute)))
+
+/* Accessor for the i'th FormData_pg_attribute element of tupdesc. */
+static inline FormData_pg_attribute *
+TupleDescAttr(TupleDesc tupdesc, int i)
+{
+	FormData_pg_attribute *attrs = TupleDescAttrAddress(tupdesc);
+
+	return &attrs[i];
+}
+
+#undef TupleDescAttrAddress
+
+/*
+ * Accessor for the i'th CompactAttribute element of tupdesc.
+ */
+static inline CompactAttribute *
+TupleDescCompactAttr(TupleDesc tupdesc, int i)
+{
+	CompactAttribute *cattr = &tupdesc->compact_attrs[i];
+#ifdef USE_ASSERT_CHECKING
+	CompactAttribute snapshot;
+
+	/*
+	 * In Assert enabled builds we verify that the CompactAttribute is
+	 * populated correctly.  This helps find bugs in places such as ALTER
+	 * TABLE where code makes changes to the FormData_pg_attribute but forgets
+	 * to call populate_compact_attribute.
+	 */
+
+	/*
+	 * Take a snapshot of how the CompactAttribute is now before calling
+	 * populate_compact_attribute to make it up-to-date with the
+	 * FormData_pg_attribute.
+	 */
+	memcpy(&snapshot, cattr, sizeof(CompactAttribute));
+
+	populate_compact_attribute(tupdesc, i);
+
+	/* reset attcacheoff back to what it was */
+	cattr->attcacheoff = snapshot.attcacheoff;
+
+	/* Ensure the snapshot matches the freshly populated CompactAttribute */
+	Assert(memcmp(&snapshot, cattr, sizeof(CompactAttribute)) == 0);
+#endif
+
+	return cattr;
+}
 
 extern TupleDesc CreateTemplateTupleDesc(int natts);
 
@@ -97,10 +200,13 @@ extern TupleDesc CreateTupleDesc(int natts, Form_pg_attribute *attrs);
 
 extern TupleDesc CreateTupleDescCopy(TupleDesc tupdesc);
 
+extern TupleDesc CreateTupleDescTruncatedCopy(TupleDesc tupdesc, int natts);
+
 extern TupleDesc CreateTupleDescCopyConstr(TupleDesc tupdesc);
 
 #define TupleDescSize(src) \
-	(offsetof(struct TupleDescData, attrs) + \
+	(offsetof(struct TupleDescData, compact_attrs) + \
+	 (src)->natts * sizeof(CompactAttribute) + \
 	 (src)->natts * sizeof(FormData_pg_attribute))
 
 extern void TupleDescCopy(TupleDesc dst, TupleDesc src);

src/include/access/tupmacs.h

@@ -30,13 +30,14 @@ att_isnull(int ATT, const bits8 *BITS)
 
 #ifndef FRONTEND
 /*
- * Given a Form_pg_attribute and a pointer into a tuple's data area,
+ * Given an attbyval and an attlen from either a Form_pg_attribute or
- * return the correct value or pointer.
+ * CompactAttribute and a pointer into a tuple's data area, return the
+ * correct value or pointer.
  *
- * We return a Datum value in all cases.  If the attribute has "byval" false,
+ * We return a Datum value in all cases.  If attbyval is false,  we return the
- * we return the same pointer into the tuple data area that we're passed.
+ * same pointer into the tuple data area that we're passed.  Otherwise, we
- * Otherwise, we return the correct number of bytes fetched from the data
+ * return the correct number of bytes fetched from the data area and extended
- * area and extended to Datum form.
+ * to Datum form.
  *
  * On machines where Datum is 8 bytes, we support fetching 8-byte byval
  * attributes; otherwise, only 1, 2, and 4-byte values are supported.

src/tools/pgindent/typedefs.list

@@ -454,6 +454,7 @@ CommitTimestampEntry
 CommitTimestampShared
 CommonEntry
 CommonTableExpr
+CompactAttribute
 CompareScalarsContext
 CompiledExprState
 CompositeIOData