Introduce CompactAttribute array in TupleDesc

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. With this change, NAMEDATALEN could be increased with a much smaller negative impact on performance. 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 Discussion: https://postgr.es/m/CAApHDvrBztXP3yx=NKNmo3xwFAFhEdyPnvrDg3=M0RhDs+4vYw@mail.gmail.com Reviewed-by: Andres Freund, Victor Yegorov
2025-11-22 12:22:45 +03:00 · 2024-12-03 16:50:59 +13:00
parent e4c8865196
commit d28dff3f6c
14 changed files with 246 additions and 68 deletions
--- a/src/backend/access/common/heaptuple.c
+++ b/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) &&
-				 VARATT_CAN_MAKE_SHORT(val))
+		else if (att->attispackable && 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 +
-			TupleDescAttr(tupleDesc, j - 1)->attlen;
+		off = TupleDescCompactAttr(tupleDesc, j - 1)->attcacheoff +
+			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++)
 	{
-
-		Form_pg_attribute attr = TupleDescAttr(tupleDesc, attnum);
+		CompactAttribute *attr = TupleDescCompactAttr(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))
 		{
--- a/src/backend/access/common/indextuple.c
+++ b/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 +
-			TupleDescAttr(tupleDesc, j - 1)->attlen;
+		off = TupleDescCompactAttr(tupleDesc, j - 1)->attcacheoff +
+			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))
 		{
@@ -588,7 +588,7 @@ index_truncate_tuple(TupleDesc sourceDescriptor, IndexTuple source,
 		return CopyIndexTuple(source);

 	/* Create temporary descriptor to scribble on */
-	truncdesc = palloc(TupleDescSize(sourceDescriptor));
+	truncdesc = CreateTemplateTupleDesc(sourceDescriptor->natts);
 	TupleDescCopy(truncdesc, sourceDescriptor);
 	truncdesc->natts = leavenatts;

--- a/src/backend/access/common/tupdesc.c
+++ b/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
+ *		Fills 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 +101,19 @@ CreateTemplateTupleDesc(int natts)
 	Assert(natts >= 0);

 	/*
-	 * Allocate enough memory for the tuple descriptor, including the
-	 * attribute rows.
+	 * Allocate enough memory for the tuple descriptor, the CompactAttribute
+	 * array and also an array of the full FormData_pg_attribute data.
 	 *
-	 * Note: the attribute array stride is sizeof(FormData_pg_attribute),
-	 * since we declare the array elements as FormData_pg_attribute for
-	 * notational convenience.  However, we only guarantee that the first
+	 * Note: the 'attrs' array stride is sizeof(FormData_pg_attribute), since
+	 * we declare the array elements as FormData_pg_attribute for notational
+	 * convenience.  However, we only guarantee that the first
 	 * ATTRIBUTE_FIXED_PART_SIZE bytes of each entry are valid; most code that
 	 * copies tupdesc entries around copies just that much.  In principle that
 	 * could be less due to trailing 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));

 	/*
@@ -96,6 +124,7 @@ CreateTemplateTupleDesc(int natts)
 	desc->tdtypeid = RECORDOID;
 	desc->tdtypmod = -1;
 	desc->tdrefcount = -1;		/* assume not reference-counted */
+	desc->attrs = TupleDescAttrAddress(desc);

 	return desc;
 }
@@ -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 +186,8 @@ 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 */
@@ -183,6 +216,9 @@ 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 +243,7 @@ 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,
@@ -252,9 +288,15 @@ 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));

+	/*
+	 * Adjust 'attrs' to point to the dst FormData_pg_attribute array rather
+	 * than the src's.
+	 */
+	dst->attrs = TupleDescAttrAddress(dst);
+
 	/*
 	 * Since we're not copying constraints and defaults, clear fields
 	 * associated with them.
@@ -268,6 +310,8 @@ TupleDescCopy(TupleDesc dst, TupleDesc src)
 		att->atthasmissing = false;
 		att->attidentity = '\0';
 		att->attgenerated = '\0';
+
+		populate_compact_attribute(dst, i);
 	}
 	dst->constr = NULL;

@@ -322,6 +366,8 @@ TupleDescCopyEntry(TupleDesc dst, AttrNumber dstAttno,
 	dstAtt->atthasmissing = false;
 	dstAtt->attidentity = '\0';
 	dstAtt->attgenerated = '\0';
+
+	populate_compact_attribute(dst, dstAttno - 1);
 }

 /*
@@ -521,7 +567,7 @@ 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 +760,8 @@ TupleDescInitEntry(TupleDesc desc,
 	att->attcompression = InvalidCompressionMethod;
 	att->attcollation = typeForm->typcollation;

+	populate_compact_attribute(desc, attributeNumber - 1);
+
 	ReleaseSysCache(tuple);
 }

@@ -821,6 +869,8 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 		default:
 			elog(ERROR, "unsupported type %u", oidtypeid);
 	}
+
+	populate_compact_attribute(desc, attributeNumber - 1);
 }

 /*