Improve handling of NULLs in KNN-GiST and KNN-SP-GiST

This commit improves subject in two ways: * It removes ugliness of 02f90879e7, which stores distance values and null flags in two separate arrays after GISTSearchItem struct. Instead we pack both distance value and null flag in IndexOrderByDistance struct. Alignment overhead should be negligible, because we typically deal with at most few "col op const" expressions in ORDER BY clause. * It fixes handling of "col op NULL" expression in KNN-SP-GiST. Now, these expression are not passed to support functions, which can't deal with them. Instead, NULL result is implicitly assumed. It future we may decide to teach support functions to deal with NULL arguments, but current solution is bugfix suitable for backpatch. Reported-by: Nikita Glukhov Discussion: https://postgr.es/m/826f57ee-afc7-8977-c44c-6111d18b02ec%40postgrespro.ru Author: Nikita Glukhov Reviewed-by: Alexander Korotkov Backpatch-through: 9.4
2019-09-19 21:30:19 +03:00 · 2019-09-19 21:30:19 +03:00 · 6cae9d2c10
parent 0a97edb12e
commit 6cae9d2c10
10 changed files with 140 additions and 101 deletions
--- a/src/backend/access/gist/gistget.c
+++ b/src/backend/access/gist/gistget.c
@ -112,9 +112,8 @@ gistkillitems(IndexScanDesc scan)
 * Similarly, *recheck_distances_p is set to indicate whether the distances
 * need to be rechecked, and it is also ignored for non-leaf entries.
 *
- * If we are doing an ordered scan, so->distancesValues[] and
- * so->distancesNulls[] is filled with distance data from the distance()
- * functions before returning success.
+ * If we are doing an ordered scan, so->distances[] is filled with distance
+ * data from the distance() functions before returning success.
 *
 * We must decompress the key in the IndexTuple before passing it to the
 * sk_funcs (which actually are the opclass Consistent or Distance methods).
@ -135,8 +134,7 @@ gistindex_keytest(IndexScanDesc scan,
 	GISTSTATE  *giststate = so->giststate;
 	ScanKey		key = scan->keyData;
 	int			keySize = scan->numberOfKeys;
-	double	   *distance_value_p;
-	bool	   *distance_null_p;
+	IndexOrderByDistance *distance_p;
 	Relation	r = scan->indexRelation;

 	*recheck_p = false;
@ -155,8 +153,8 @@ gistindex_keytest(IndexScanDesc scan,
 			elog(ERROR, "invalid GiST tuple found on leaf page");
 		for (i = 0; i < scan->numberOfOrderBys; i++)
 		{
-			so->distanceValues[i] = -get_float8_infinity();
-			so->distanceNulls[i] = false;
+			so->distances[i].value = -get_float8_infinity();
+			so->distances[i].isnull = false;
 		}
 		return true;
 	}
@ -240,8 +238,7 @@ gistindex_keytest(IndexScanDesc scan,

 	/* OK, it passes --- now let's compute the distances */
 	key = scan->orderByData;
-	distance_value_p = so->distanceValues;
-	distance_null_p = so->distanceNulls;
+	distance_p = so->distances;
 	keySize = scan->numberOfOrderBys;
 	while (keySize > 0)
 	{
@ -256,8 +253,8 @@ gistindex_keytest(IndexScanDesc scan,
 		if ((key->sk_flags & SK_ISNULL) || isNull)
 		{
 			/* Assume distance computes as null */
-			*distance_value_p = 0.0;
-			*distance_null_p = true;
+			distance_p->value = 0.0;
+			distance_p->isnull = true;
 		}
 		else
 		{
@ -294,13 +291,12 @@ gistindex_keytest(IndexScanDesc scan,
 									 ObjectIdGetDatum(key->sk_subtype),
 									 PointerGetDatum(&recheck));
 			*recheck_distances_p |= recheck;
-			*distance_value_p = DatumGetFloat8(dist);
-			*distance_null_p = false;
+			distance_p->value = DatumGetFloat8(dist);
+			distance_p->isnull = false;
 		}

 		key++;
-		distance_value_p++;
-		distance_null_p++;
+		distance_p++;
 		keySize--;
 	}

@ -313,8 +309,7 @@ gistindex_keytest(IndexScanDesc scan,
 *
 * scan: index scan we are executing
 * pageItem: search queue item identifying an index page to scan
- * myDistanceValues: distances array associated with pageItem, or NULL at the root
- * myDistanceNulls: null flags for myDistanceValues array, or NULL at the root
+ * myDistances: distances array associated with pageItem, or NULL at the root
 * tbm: if not NULL, gistgetbitmap's output bitmap
 * ntids: if not NULL, gistgetbitmap's output tuple counter
 *
@ -332,8 +327,7 @@ gistindex_keytest(IndexScanDesc scan,
 */
 static void
 gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
-			 double *myDistanceValues, bool *myDistanceNulls,
-			 TIDBitmap *tbm, int64 *ntids)
+			 IndexOrderByDistance *myDistances, TIDBitmap *tbm, int64 *ntids)
 {
 	GISTScanOpaque so = (GISTScanOpaque) scan->opaque;
 	GISTSTATE  *giststate = so->giststate;
@ -370,7 +364,7 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
 		GISTSearchItem *item;

 		/* This can't happen when starting at the root */
-		Assert(myDistanceValues != NULL && myDistanceNulls != NULL);
+		Assert(myDistances != NULL);

 		oldcxt = MemoryContextSwitchTo(so->queueCxt);

@ -380,10 +374,8 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
 		item->data.parentlsn = pageItem->data.parentlsn;

 		/* Insert it into the queue using same distances as for this page */
-		memcpy(GISTSearchItemDistanceValues(item, scan->numberOfOrderBys),
-			   myDistanceValues, sizeof(double) * scan->numberOfOrderBys);
-		memcpy(GISTSearchItemDistanceNulls(item, scan->numberOfOrderBys),
-			   myDistanceNulls, sizeof(bool) * scan->numberOfOrderBys);
+		memcpy(item->distances, myDistances,
+			   sizeof(item->distances[0]) * scan->numberOfOrderBys);

 		pairingheap_add(so->queue, &item->phNode);

@ -527,10 +519,8 @@ gistScanPage(IndexScanDesc scan, GISTSearchItem *pageItem,
 			}

 			/* Insert it into the queue using new distance data */
-			memcpy(GISTSearchItemDistanceValues(item, nOrderBys),
-				   so->distanceValues, sizeof(double) * nOrderBys);
-			memcpy(GISTSearchItemDistanceNulls(item, nOrderBys),
-				   so->distanceNulls, sizeof(bool) * nOrderBys);
+			memcpy(item->distances, so->distances,
+				   sizeof(item->distances[0]) * nOrderBys);

 			pairingheap_add(so->queue, &item->phNode);

@ -595,8 +585,7 @@ getNextNearest(IndexScanDesc scan)
 			scan->xs_recheck = item->data.heap.recheck;

 			index_store_float8_orderby_distances(scan, so->orderByTypes,
-												 GISTSearchItemDistanceValues(item, scan->numberOfOrderBys),
-												 GISTSearchItemDistanceNulls(item, scan->numberOfOrderBys),
+												 item->distances,
 												 item->data.heap.recheckDistances);

 			/* in an index-only scan, also return the reconstructed tuple. */
@ -609,10 +598,7 @@ getNextNearest(IndexScanDesc scan)
 			/* visit an index page, extract its items into queue */
 			CHECK_FOR_INTERRUPTS();

-			gistScanPage(scan, item,
-						 GISTSearchItemDistanceValues(item, scan->numberOfOrderBys),
-						 GISTSearchItemDistanceNulls(item, scan->numberOfOrderBys),
-						 NULL, NULL);
+			gistScanPage(scan, item, item->distances, NULL, NULL);
 		}

 		pfree(item);
@ -650,7 +636,7 @@ gistgettuple(IndexScanDesc scan, ScanDirection dir)

 		fakeItem.blkno = GIST_ROOT_BLKNO;
 		memset(&fakeItem.data.parentlsn, 0, sizeof(GistNSN));
-		gistScanPage(scan, &fakeItem, NULL, NULL, NULL, NULL);
+		gistScanPage(scan, &fakeItem, NULL, NULL, NULL);
 	}

 	if (scan->numberOfOrderBys > 0)
@ -744,10 +730,7 @@ gistgettuple(IndexScanDesc scan, ScanDirection dir)
 				 * this page, we fall out of the inner "do" and loop around to
 				 * return them.
 				 */
-				gistScanPage(scan, item,
-							 GISTSearchItemDistanceValues(item, scan->numberOfOrderBys),
-							 GISTSearchItemDistanceNulls(item, scan->numberOfOrderBys),
-							 NULL, NULL);
+				gistScanPage(scan, item, item->distances, NULL, NULL);

 				pfree(item);
 			} while (so->nPageData == 0);
@ -778,7 +761,7 @@ gistgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)

 	fakeItem.blkno = GIST_ROOT_BLKNO;
 	memset(&fakeItem.data.parentlsn, 0, sizeof(GistNSN));
-	gistScanPage(scan, &fakeItem, NULL, NULL, tbm, &ntids);
+	gistScanPage(scan, &fakeItem, NULL, tbm, &ntids);

 	/*
 	 * While scanning a leaf page, ItemPointers of matching heap tuples will
@ -793,10 +776,7 @@ gistgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)

 		CHECK_FOR_INTERRUPTS();

-		gistScanPage(scan, item,
-					 GISTSearchItemDistanceValues(item, scan->numberOfOrderBys),
-					 GISTSearchItemDistanceNulls(item, scan->numberOfOrderBys),
-					 tbm, &ntids);
+		gistScanPage(scan, item, item->distances, tbm, &ntids);

 		pfree(item);
 	}
--- a/src/backend/access/gist/gistscan.c
+++ b/src/backend/access/gist/gistscan.c
@ -33,26 +33,23 @@ pairingheap_GISTSearchItem_cmp(const pairingheap_node *a, const pairingheap_node
 	const GISTSearchItem *sb = (const GISTSearchItem *) b;
 	IndexScanDesc scan = (IndexScanDesc) arg;
 	int			i;
-	double	   *da = GISTSearchItemDistanceValues(sa, scan->numberOfOrderBys),
-			   *db = GISTSearchItemDistanceValues(sb, scan->numberOfOrderBys);
-	bool	   *na = GISTSearchItemDistanceNulls(sa, scan->numberOfOrderBys),
-			   *nb = GISTSearchItemDistanceNulls(sb, scan->numberOfOrderBys);

 	/* Order according to distance comparison */
 	for (i = 0; i < scan->numberOfOrderBys; i++)
 	{
-		if (na[i])
+		if (sa->distances[i].isnull)
 		{
-			if (!nb[i])
+			if (!sb->distances[i].isnull)
 				return -1;
 		}
-		else if (nb[i])
+		else if (sb->distances[i].isnull)
 		{
 			return 1;
 		}
 		else
 		{
-			int			cmp = -float8_cmp_internal(da[i], db[i]);
+			int			cmp = -float8_cmp_internal(sa->distances[i].value,
+												   sb->distances[i].value);

 			if (cmp != 0)
 				return cmp;
@ -100,8 +97,7 @@ gistbeginscan(Relation r, int nkeys, int norderbys)
 	so->queueCxt = giststate->scanCxt;	/* see gistrescan */

 	/* workspaces with size dependent on numberOfOrderBys: */
-	so->distanceValues = palloc(sizeof(double) * scan->numberOfOrderBys);
-	so->distanceNulls = palloc(sizeof(bool) * scan->numberOfOrderBys);
+	so->distances = palloc(sizeof(so->distances[0]) * scan->numberOfOrderBys);
 	so->qual_ok = true;			/* in case there are zero keys */
 	if (scan->numberOfOrderBys > 0)
 	{
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@ -847,14 +847,14 @@ index_getprocinfo(Relation irel,
 */
 void
 index_store_float8_orderby_distances(IndexScanDesc scan, Oid *orderByTypes,
-									 double *distanceValues,
-									 bool *distanceNulls, bool recheckOrderBy)
+									 IndexOrderByDistance *distances,
+									 bool recheckOrderBy)
 {
 	int			i;

 	scan->xs_recheckorderby = recheckOrderBy;

-	if (!distanceValues)
+	if (!distances)
 	{
 		Assert(!scan->xs_recheckorderby);

@ -869,11 +869,11 @@ index_store_float8_orderby_distances(IndexScanDesc scan, Oid *orderByTypes,

 	for (i = 0; i < scan->numberOfOrderBys; i++)
 	{
-		if (distanceNulls && distanceNulls[i])
-		{
+		scan->xs_orderbynulls[i] = distances[i].isnull;
+
+		if (scan->xs_orderbynulls[i])
 			scan->xs_orderbyvals[i] = (Datum) 0;
-			scan->xs_orderbynulls[i] = true;
-		}
+
 		if (orderByTypes[i] == FLOAT8OID)
 		{
 #ifndef USE_FLOAT8_BYVAL
@ -881,8 +881,8 @@ index_store_float8_orderby_distances(IndexScanDesc scan, Oid *orderByTypes,
 			if (!scan->xs_orderbynulls[i])
 				pfree(DatumGetPointer(scan->xs_orderbyvals[i]));
 #endif
-			scan->xs_orderbyvals[i] = Float8GetDatum(distanceValues[i]);
-			scan->xs_orderbynulls[i] = false;
+			if (!scan->xs_orderbynulls[i])
+				scan->xs_orderbyvals[i] = Float8GetDatum(distances[i].value);
 		}
 		else if (orderByTypes[i] == FLOAT4OID)
 		{
@ -892,8 +892,8 @@ index_store_float8_orderby_distances(IndexScanDesc scan, Oid *orderByTypes,
 			if (!scan->xs_orderbynulls[i])
 				pfree(DatumGetPointer(scan->xs_orderbyvals[i]));
 #endif
-			scan->xs_orderbyvals[i] = Float4GetDatum((float4) distanceValues[i]);
-			scan->xs_orderbynulls[i] = false;
+			if (!scan->xs_orderbynulls[i])
+				scan->xs_orderbyvals[i] = Float4GetDatum((float4) distances[i].value);
 		}
 		else
 		{
--- a/src/backend/access/spgist/spgscan.c
+++ b/src/backend/access/spgist/spgscan.c
@ -107,13 +107,13 @@ spgAllocSearchItem(SpGistScanOpaque so, bool isnull, double *distances)
 {
 	/* allocate distance array only for non-NULL items */
 	SpGistSearchItem *item =
-	palloc(SizeOfSpGistSearchItem(isnull ? 0 : so->numberOfOrderBys));
+	palloc(SizeOfSpGistSearchItem(isnull ? 0 : so->numberOfNonNullOrderBys));

 	item->isNull = isnull;

-	if (!isnull && so->numberOfOrderBys > 0)
+	if (!isnull && so->numberOfNonNullOrderBys > 0)
 		memcpy(item->distances, distances,
-			   so->numberOfOrderBys * sizeof(double));
+			   sizeof(item->distances[0]) * so->numberOfNonNullOrderBys);

 	return item;
 }
@ -208,6 +208,34 @@ spgPrepareScanKeys(IndexScanDesc scan)
 	so->numberOfOrderBys = scan->numberOfOrderBys;
 	so->orderByData = scan->orderByData;

+	if (so->numberOfOrderBys <= 0)
+		so->numberOfNonNullOrderBys = 0;
+	else
+	{
+		int			j = 0;
+
+		/*
+		 * Remove all NULL keys, but remember their offsets in the original
+		 * array.
+		 */
+		for (i = 0; i < scan->numberOfOrderBys; i++)
+		{
+			ScanKey		skey = &so->orderByData[i];
+
+			if (skey->sk_flags & SK_ISNULL)
+				so->nonNullOrderByOffsets[i] = -1;
+			else
+			{
+				if (i != j)
+					so->orderByData[j] = *skey;
+
+				so->nonNullOrderByOffsets[i] = j++;
+			}
+		}
+
+		so->numberOfNonNullOrderBys = j;
+	}
+
 	if (scan->numberOfKeys <= 0)
 	{
 		/* If no quals, whole-index scan is required */
@ -295,6 +323,8 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
 		/* This will be filled in spgrescan, but allocate the space here */
 		so->orderByTypes = (Oid *)
 			palloc(sizeof(Oid) * scan->numberOfOrderBys);
+		so->nonNullOrderByOffsets = (int *)
+			palloc(sizeof(int) * scan->numberOfOrderBys);

 		/* These arrays have constant contents, so we can fill them now */
 		so->zeroDistances = (double *)
@ -394,6 +424,7 @@ spgendscan(IndexScanDesc scan)
 	if (scan->numberOfOrderBys > 0)
 	{
 		pfree(so->orderByTypes);
+		pfree(so->nonNullOrderByOffsets);
 		pfree(so->zeroDistances);
 		pfree(so->infDistances);
 		pfree(scan->xs_orderbyvals);
@ -465,7 +496,7 @@ spgLeafTest(SpGistScanOpaque so, SpGistSearchItem *item,
 		in.scankeys = so->keyData;
 		in.nkeys = so->numberOfKeys;
 		in.orderbys = so->orderByData;
-		in.norderbys = so->numberOfOrderBys;
+		in.norderbys = so->numberOfNonNullOrderBys;
 		in.reconstructedValue = item->value;
 		in.traversalValue = item->traversalValue;
 		in.level = item->level;
@ -492,7 +523,7 @@ spgLeafTest(SpGistScanOpaque so, SpGistSearchItem *item,
 	if (result)
 	{
 		/* item passes the scankeys */
-		if (so->numberOfOrderBys > 0)
+		if (so->numberOfNonNullOrderBys > 0)
 		{
 			/* the scan is ordered -> add the item to the queue */
 			MemoryContext oldCxt = MemoryContextSwitchTo(so->traversalCxt);
@ -531,7 +562,7 @@ spgInitInnerConsistentIn(spgInnerConsistentIn *in,
 	in->scankeys = so->keyData;
 	in->orderbys = so->orderByData;
 	in->nkeys = so->numberOfKeys;
-	in->norderbys = so->numberOfOrderBys;
+	in->norderbys = so->numberOfNonNullOrderBys;
 	in->reconstructedValue = item->value;
 	in->traversalMemoryContext = so->traversalCxt;
 	in->traversalValue = item->traversalValue;
@ -751,7 +782,7 @@ redirect:
 		if (item->isLeaf)
 		{
 			/* We store heap items in the queue only in case of ordered search */
-			Assert(so->numberOfOrderBys > 0);
+			Assert(so->numberOfNonNullOrderBys > 0);
 			storeRes(so, &item->heapPtr, item->value, item->isNull,
 					 item->recheck, item->recheckDistances, item->distances);
 			reportedSome = true;
@ -874,7 +905,7 @@ spggetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
 static void
 storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,
 			  Datum leafValue, bool isnull, bool recheck, bool recheckDistances,
-			  double *distances)
+			  double *nonNullDistances)
 {
 	Assert(so->nPtrs < MaxIndexTuplesPerPage);
 	so->heapPtrs[so->nPtrs] = *heapPtr;
@ -883,13 +914,33 @@ storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,

 	if (so->numberOfOrderBys > 0)
 	{
-		if (isnull)
+		if (isnull || so->numberOfNonNullOrderBys <= 0)
 			so->distances[so->nPtrs] = NULL;
 		else
 		{
-			Size		size = sizeof(double) * so->numberOfOrderBys;
+			IndexOrderByDistance *distances =
+			palloc(sizeof(distances[0]) * so->numberOfOrderBys);
+			int			i;

-			so->distances[so->nPtrs] = memcpy(palloc(size), distances, size);
+			for (i = 0; i < so->numberOfOrderBys; i++)
+			{
+				int			offset = so->nonNullOrderByOffsets[i];
+
+				if (offset >= 0)
+				{
+					/* Copy non-NULL distance value */
+					distances[i].value = nonNullDistances[offset];
+					distances[i].isnull = false;
+				}
+				else
+				{
+					/* Set distance's NULL flag. */
+					distances[i].value = 0.0;
+					distances[i].isnull = true;
+				}
+			}
+
+			so->distances[so->nPtrs] = distances;
 		}
 	}

@ -929,7 +980,6 @@ spggettuple(IndexScanDesc scan, ScanDirection dir)
 			if (so->numberOfOrderBys > 0)
 				index_store_float8_orderby_distances(scan, so->orderByTypes,
 													 so->distances[so->iPtr],
-													 NULL,
 													 so->recheckDistances[so->iPtr]);
 			so->iPtr++;
 			return true;
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@ -118,6 +118,13 @@ typedef enum IndexUniqueCheck
 } IndexUniqueCheck;


+/* Nullable "ORDER BY col op const" distance */
+typedef struct IndexOrderByDistance
+{
+	double		value;
+	bool		isnull;
+} IndexOrderByDistance;
+
 /*
 * generalized index_ interface routines (in indexam.c)
 */
@ -179,8 +186,7 @@ extern FmgrInfo *index_getprocinfo(Relation irel, AttrNumber attnum,
 								   uint16 procnum);
 extern void index_store_float8_orderby_distances(IndexScanDesc scan,
 												 Oid *orderByTypes,
-												 double *distanceValues,
-												 bool *distanceNulls,
+												 IndexOrderByDistance *distances,
 												 bool recheckOrderBy);

 /*
--- a/src/include/access/gist_private.h
+++ b/src/include/access/gist_private.h
@ -138,29 +138,15 @@ typedef struct GISTSearchItem
 		GISTSearchHeapItem heap;	/* heap info, if heap tuple */
 	}			data;

-	/*
-	 * This data structure is followed by arrays of distance values and
-	 * distance null flags.  Size of both arrays is
-	 * IndexScanDesc->numberOfOrderBys. See macros below for accessing those
-	 * arrays.
-	 */
+	/* numberOfOrderBys entries */
+	IndexOrderByDistance distances[FLEXIBLE_ARRAY_MEMBER];
 } GISTSearchItem;

 #define GISTSearchItemIsHeap(item)	((item).blkno == InvalidBlockNumber)

-#define SizeOfGISTSearchItem(n_distances) (DOUBLEALIGN(sizeof(GISTSearchItem)) + \
-	(sizeof(double) + sizeof(bool)) * (n_distances))
-
-/*
- * We actually don't need n_distances compute pointer to distance values.
- * Nevertheless take n_distances as argument to have same arguments list for
- * GISTSearchItemDistanceValues() and GISTSearchItemDistanceNulls().
- */
-#define GISTSearchItemDistanceValues(item, n_distances) \
-	((double *) ((Pointer) (item) + DOUBLEALIGN(sizeof(GISTSearchItem))))
-
-#define GISTSearchItemDistanceNulls(item, n_distances) \
-	((bool *) ((Pointer) (item) + DOUBLEALIGN(sizeof(GISTSearchItem)) + sizeof(double) * (n_distances)))
+#define SizeOfGISTSearchItem(n_distances) \
+	(offsetof(GISTSearchItem, distances) + \
+	 sizeof(IndexOrderByDistance) * (n_distances))

 /*
 * GISTScanOpaqueData: private state for a scan of a GiST index
@ -176,8 +162,7 @@ typedef struct GISTScanOpaqueData
 	bool		firstCall;		/* true until first gistgettuple call */

 	/* pre-allocated workspace arrays */
-	double	   *distanceValues; /* output area for gistindex_keytest */
-	bool	   *distanceNulls;
+	IndexOrderByDistance *distances;	/* output area for gistindex_keytest */

 	/* info about killed items if any (killedItems is NULL if never used) */
 	OffsetNumber *killedItems;	/* offset numbers of killed items */
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@ -169,8 +169,12 @@ typedef struct SpGistScanOpaqueData
 	int			numberOfKeys;	/* number of index qualifier conditions */
 	ScanKey		keyData;		/* array of index qualifier descriptors */
 	int			numberOfOrderBys;	/* number of ordering operators */
+	int			numberOfNonNullOrderBys;	/* number of ordering operators
+											 * with non-NULL arguments */
 	ScanKey		orderByData;	/* array of ordering op descriptors */
 	Oid		   *orderByTypes;	/* array of ordering op return types */
+	int		   *nonNullOrderByOffsets;	/* array of offset of non-NULL
+										 * ordering keys in the original array */
 	Oid			indexCollation; /* collation of index column */

 	/* Opclass defined functions: */
@ -195,7 +199,9 @@ typedef struct SpGistScanOpaqueData
 	bool		recheckDistances[MaxIndexTuplesPerPage];	/* distance recheck
 															 * flags */
 	HeapTuple	reconTups[MaxIndexTuplesPerPage];	/* reconstructed tuples */
-	double	   *distances[MaxIndexTuplesPerPage];	/* distances (for recheck) */
+
+	/* distances (for recheck) */
+	IndexOrderByDistance *distances[MaxIndexTuplesPerPage];

 	/*
 	 * Note: using MaxIndexTuplesPerPage above is a bit hokey since
--- a/src/test/regress/expected/create_index_spgist.out
+++ b/src/test/regress/expected/create_index_spgist.out
@ -555,6 +555,16 @@ WHERE seq.dist IS DISTINCT FROM idx.dist;
 ---+------+---+---+------+---
 (0 rows)

+-- check ORDER BY distance to NULL
+SELECT (SELECT p FROM kd_point_tbl ORDER BY p <-> pt LIMIT 1)
+FROM (VALUES (point '1,2'), (NULL), ('1234,5678')) pts(pt);
+      p      
+-------------
+ (59,21)
+ (9853,112)
+ (1239,5647)
+(3 rows)
+
 EXPLAIN (COSTS OFF)
 SELECT count(*) FROM radix_text_tbl WHERE t = 'P0123456789abcdef';
                         QUERY PLAN                         
--- a/src/test/regress/sql/create_index_spgist.sql
+++ b/src/test/regress/sql/create_index_spgist.sql
@ -225,6 +225,11 @@ SELECT * FROM quad_point_tbl_ord_seq3 seq FULL JOIN kd_point_tbl_ord_idx3 idx
 ON seq.n = idx.n
 WHERE seq.dist IS DISTINCT FROM idx.dist;

+-- check ORDER BY distance to NULL
+SELECT (SELECT p FROM kd_point_tbl ORDER BY p <-> pt LIMIT 1)
+FROM (VALUES (point '1,2'), (NULL), ('1234,5678')) pts(pt);
+
+
 EXPLAIN (COSTS OFF)
 SELECT count(*) FROM radix_text_tbl WHERE t = 'P0123456789abcdef';
 SELECT count(*) FROM radix_text_tbl WHERE t = 'P0123456789abcdef';
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@ -1043,6 +1043,7 @@ IndexList
 IndexOnlyScan
 IndexOnlyScanState
 IndexOptInfo
+IndexOrderByDistance
 IndexPath
 IndexRuntimeKeyInfo
 IndexScan