0004-Add-kNN-support-to-SP-GiST-v01.patch

diff --git a/doc/src/sgml/spgist.sgml b/doc/src/sgml/spgist.sgml
index cd4a8d0..53ca8bf 100644
--- a/doc/src/sgml/spgist.sgml
+++ b/doc/src/sgml/spgist.sgml
@@ -584,7 +584,9 @@ CREATE FUNCTION my_inner_consistent(internal, internal) RETURNS void ...
 typedef struct spgInnerConsistentIn
 {
     ScanKey     scankeys;       /* array of operators and comparison values */
+    ScanKey		orderbyKeys;	/* array of ordering operators and comparison values */
     int         nkeys;          /* length of array */
+    int         norderbys;      /* length of array */
 
     Datum       reconstructedValue;     /* value reconstructed at parent */
     void       *traversalValue; /* opclass-specific traverse value */
@@ -607,6 +609,7 @@ typedef struct spgInnerConsistentOut
     int        *levelAdds;      /* increment level by this much for each */
     Datum      *reconstructedValues;    /* associated reconstructed values */
     void      **traversalValues;        /* opclass-specific traverse values */
+    double    **distances;              /* associated distances */
 } spgInnerConsistentOut;
 </programlisting>
 
@@ -621,6 +624,8 @@ typedef struct spgInnerConsistentOut
        In particular it is not necessary to check <structfield>sk_flags</> to
        see if the comparison value is NULL, because the SP-GiST core code
        will filter out such conditions.
+       <structfield>orderbyKeys</>, of length <structfield>norderbys</>,
+       describes ordering operators (if any) in the same fashion.
        <structfield>reconstructedValue</> is the value reconstructed for the
        parent tuple; it is <literal>(Datum) 0</> at the root level or if the
        <function>inner_consistent</> function did not provide a value at the
@@ -661,6 +666,11 @@ typedef struct spgInnerConsistentOut
        <structfield>reconstructedValues</> to an array of the values
        reconstructed for each child node to be visited; otherwise, leave
        <structfield>reconstructedValues</> as NULL.
+       <structfield>distances</> if the ordered search is carried out,
+       the implementation is supposed to fill them in accordance to the
+       ordering operators provided in <structfield>orderbyKeys</>
+       (nodes with lowest distances will be processed first). Leave it
+       NULL otherwise.
        If it is desired to pass down additional out-of-band information
        (<quote>traverse values</>) to lower levels of the tree search,
        set <structfield>traversalValues</> to an array of the appropriate
@@ -669,7 +679,7 @@ typedef struct spgInnerConsistentOut
        Note that the <function>inner_consistent</> function is
        responsible for palloc'ing the
        <structfield>nodeNumbers</>, <structfield>levelAdds</>,
-       <structfield>reconstructedValues</>, and
+       <structfield>distances</>, <structfield>reconstructedValues</> and
        <structfield>traversalValues</> arrays in the current memory context.
        However, any output traverse values pointed to by
        the <structfield>traversalValues</> array should be allocated
@@ -699,7 +709,9 @@ CREATE FUNCTION my_leaf_consistent(internal, internal) RETURNS bool ...
 typedef struct spgLeafConsistentIn
 {
     ScanKey     scankeys;       /* array of operators and comparison values */
-    int         nkeys;          /* length of array */
+    ScanKey     orderbykeys;    /* array of ordering operators and comparison values */
+    int         nkeys;          /* length of scankeys array */
+    int         norderbys;      /* length of orderbykeys array */
 
     Datum       reconstructedValue;     /* value reconstructed at parent */
     void       *traversalValue; /* opclass-specific traverse value */
@@ -711,8 +723,10 @@ typedef struct spgLeafConsistentIn
 
 typedef struct spgLeafConsistentOut
 {
-    Datum       leafValue;      /* reconstructed original data, if any */
-    bool        recheck;        /* set true if operator must be rechecked */
+    Datum       leafValue;        /* reconstructed original data, if any */
+    bool        recheck;          /* set true if operator must be rechecked */
+    bool        recheckDistances; /* set true if distances must be rechecked */
+    double     *distances;        /* associated distances */
 } spgLeafConsistentOut;
 </programlisting>
 
@@ -727,6 +741,8 @@ typedef struct spgLeafConsistentOut
        In particular it is not necessary to check <structfield>sk_flags</> to
        see if the comparison value is NULL, because the SP-GiST core code
        will filter out such conditions.
+       The array <structfield>orderbykeys>, of length <structfield>norderbys</>,
+       describes the ordering operators in the same fashion.
        <structfield>reconstructedValue</> is the value reconstructed for the
        parent tuple; it is <literal>(Datum) 0</> at the root level or if the
        <function>inner_consistent</> function did not provide a value at the
@@ -752,6 +768,13 @@ typedef struct spgLeafConsistentOut
        <structfield>recheck</> may be set to <literal>true</> if the match
        is uncertain and so the operator(s) must be re-applied to the actual
        heap tuple to verify the match.
+       In case when the ordered search is performed, <structfield>distances</>
+       should be set in accordance with the ordering operator provided, otherwise
+       implementation is supposed to set it to NULL.
+       If at least one of returned distances is not exact, the function must set
+       <structfield>recheckDistances</> to true.  In this case the executor will
+       calculate the accurate distance after fetching the tuple from the heap,
+       and reorder the tuples if necessary.       
       </para>
      </listitem>
     </varlistentry>
diff --git a/src/backend/access/spgist/Makefile b/src/backend/access/spgist/Makefile
index 14948a5..5be3df5 100644
--- a/src/backend/access/spgist/Makefile
+++ b/src/backend/access/spgist/Makefile
@@ -14,6 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 OBJS = spgutils.o spginsert.o spgscan.o spgvacuum.o spgvalidate.o \
 	spgdoinsert.o spgxlog.o \
-	spgtextproc.o spgquadtreeproc.o spgkdtreeproc.o
+	spgtextproc.o spgquadtreeproc.o spgkdtreeproc.o \
+	spgproc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/spgist/README b/src/backend/access/spgist/README
index 09ab21a..1420a18 100644
--- a/src/backend/access/spgist/README
+++ b/src/backend/access/spgist/README
@@ -41,7 +41,12 @@ contain exactly one inner tuple.
 
 When the search traversal algorithm reaches an inner tuple, it chooses a set
 of nodes to continue tree traverse in depth.  If it reaches a leaf page it
-scans a list of leaf tuples to find the ones that match the query.
+scans a list of leaf tuples to find the ones that match the query. SP-GiSTs
+also support ordered searches - that is during the scan is performed,
+implementation can choose to map floating-point distances to inner and leaf
+tuples and the traversal will be performed by the closest-first model. It
+can be usefull e.g. for performing nearest-neighbour searches on the dataset.
+
 
 The insertion algorithm descends the tree similarly, except it must choose
 just one node to descend to from each inner tuple.  Insertion might also have
@@ -371,3 +376,4 @@ AUTHORS
 
     Teodor Sigaev <teodor@sigaev.ru>
     Oleg Bartunov <oleg@sai.msu.su>
+    Vlad Sterzhanov <gliderok@gmail.com>
diff --git a/src/backend/access/spgist/spgscan.c b/src/backend/access/spgist/spgscan.c
index 139d998..f585b62 100644
--- a/src/backend/access/spgist/spgscan.c
+++ b/src/backend/access/spgist/spgscan.c
@@ -15,79 +15,118 @@
 
 #include "postgres.h"
 
+#include "access/genam.h"
 #include "access/relscan.h"
 #include "access/spgist_private.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
+#include "utils/builtins.h"
 #include "utils/datum.h"
+#include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
 
 typedef void (*storeRes_func) (SpGistScanOpaque so, ItemPointer heapPtr,
-								 Datum leafValue, bool isnull, bool recheck);
+							   Datum leafValue, bool isnull, bool recheck,
+							   bool recheckDist, double *distances);
 
-typedef struct ScanStackEntry
+/*
+ * Pairing heap comparison function for the SpGistSearchItem queue
+ */
+static int
+pairingheap_SpGistSearchItem_cmp(const pairingheap_node *a,
+								 const pairingheap_node *b, void *arg)
 {
-	Datum		reconstructedValue;		/* value reconstructed from parent */
-	void	   *traversalValue; /* opclass-specific traverse value */
-	int			level;			/* level of items on this page */
-	ItemPointerData ptr;		/* block and offset to scan from */
-} ScanStackEntry;
+	const SpGistSearchItem *sa = (const SpGistSearchItem *) a;
+	const SpGistSearchItem *sb = (const SpGistSearchItem *) b;
+	IndexScanDesc scan = (IndexScanDesc) arg;
+	int			i;
+
+	/* Order according to distance comparison */
+	for (i = 0; i < scan->numberOfOrderBys; i++)
+	{
+		if (sa->distances[i] != sb->distances[i])
+			return (sa->distances[i] < sb->distances[i]) ? 1 : -1;
+	}
 
+	/* Leaf items go before inner pages, to ensure a depth-first search */
+	if (sa->isLeaf && !sb->isLeaf)
+		return 1;
+	if (!sa->isLeaf && sb->isLeaf)
+		return -1;
+
+	return 0;
+}
 
-/* Free a ScanStackEntry */
 static void
-freeScanStackEntry(SpGistScanOpaque so, ScanStackEntry *stackEntry)
+spgFreeSearchItem(SpGistScanOpaque so, SpGistSearchItem *item)
 {
 	if (!so->state.attType.attbyval &&
-		DatumGetPointer(stackEntry->reconstructedValue) != NULL)
-		pfree(DatumGetPointer(stackEntry->reconstructedValue));
-	if (stackEntry->traversalValue)
-		pfree(stackEntry->traversalValue);
+		DatumGetPointer(item->value) != NULL)
+		pfree(DatumGetPointer(item->value));
+
+	if (item->traversalValue)
+		pfree(item->traversalValue);
 
-	pfree(stackEntry);
+	pfree(item);
+}
+
+/*
+ * Add SpGistSearchItem to queue
+ *
+ * Called in queue context
+ */
+static void
+spgAddSearchItemToQueue(SpGistScanOpaque so, SpGistSearchItem *item,
+						double *distances)
+{
+	memcpy(item->distances, distances, so->numberOfOrderBys * sizeof(double));
+	pairingheap_add(so->queue, &item->phNode);
 }
 
-/* Free the entire stack */
 static void
-freeScanStack(SpGistScanOpaque so)
+spgAddStartItem(SpGistScanOpaque so, bool isnull)
 {
-	ListCell   *lc;
+	SpGistSearchItem *startEntry = (SpGistSearchItem *) palloc0(
+								SizeOfSpGistSearchItem(so->numberOfOrderBys));
 
-	foreach(lc, so->scanStack)
-	{
-		freeScanStackEntry(so, (ScanStackEntry *) lfirst(lc));
-	}
-	list_free(so->scanStack);
-	so->scanStack = NIL;
+	ItemPointerSet(&startEntry->heap,
+				   isnull ? SPGIST_NULL_BLKNO : SPGIST_ROOT_BLKNO,
+				   FirstOffsetNumber);
+	startEntry->isLeaf = false;
+	startEntry->level = 0;
+	startEntry->isnull = isnull;
+
+	spgAddSearchItemToQueue(so, startEntry, so->zeroDistances);
 }
 
 /*
- * Initialize scanStack to search the root page, resetting
+ * Initialize queue to search the root page, resetting
  * any previously active scan
  */
 static void
 resetSpGistScanOpaque(SpGistScanOpaque so)
 {
-	ScanStackEntry *startEntry;
-
-	freeScanStack(so);
+	MemoryContext oldCtx = MemoryContextSwitchTo(so->queueCxt);
 
 	if (so->searchNulls)
-	{
-		/* Stack a work item to scan the null index entries */
-		startEntry = (ScanStackEntry *) palloc0(sizeof(ScanStackEntry));
-		ItemPointerSet(&startEntry->ptr, SPGIST_NULL_BLKNO, FirstOffsetNumber);
-		so->scanStack = lappend(so->scanStack, startEntry);
-	}
+		/* Add a work item to scan the null index entries */
+		spgAddStartItem(so, true);
 
 	if (so->searchNonNulls)
+		/* Add a work item to scan the non-null index entries */
+		spgAddStartItem(so, false);
+
+	MemoryContextSwitchTo(oldCtx);
+
+	if (so->numberOfOrderBys > 0)
 	{
-		/* Stack a work item to scan the non-null index entries */
-		startEntry = (ScanStackEntry *) palloc0(sizeof(ScanStackEntry));
-		ItemPointerSet(&startEntry->ptr, SPGIST_ROOT_BLKNO, FirstOffsetNumber);
-		so->scanStack = lappend(so->scanStack, startEntry);
+		/* Must pfree distances to avoid memory leak */
+		int			i;
+
+		for (i = 0; i < so->nPtrs; i++)
+			pfree(so->distances[i]);
 	}
 
 	if (so->want_itup)
@@ -122,6 +161,9 @@ spgPrepareScanKeys(IndexScanDesc scan)
 	int			nkeys;
 	int			i;
 
+	so->numberOfOrderBys = scan->numberOfOrderBys;
+	so->orderByData = scan->orderByData;
+
 	if (scan->numberOfKeys <= 0)
 	{
 		/* If no quals, whole-index scan is required */
@@ -182,8 +224,9 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
 {
 	IndexScanDesc scan;
 	SpGistScanOpaque so;
+	int			i;
 
-	scan = RelationGetIndexScan(rel, keysz, 0);
+	scan = RelationGetIndexScan(rel, keysz, orderbysz);
 
 	so = (SpGistScanOpaque) palloc0(sizeof(SpGistScanOpaqueData));
 	if (keysz > 0)
@@ -191,6 +234,7 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
 	else
 		so->keyData = NULL;
 	initSpGistState(&so->state, scan->indexRelation);
+
 	so->tempCxt = AllocSetContextCreate(CurrentMemoryContext,
 										"SP-GiST search temporary context",
 										ALLOCSET_DEFAULT_SIZES);
@@ -198,6 +242,36 @@ spgbeginscan(Relation rel, int keysz, int orderbysz)
 	/* Set up indexTupDesc and xs_itupdesc in case it's an index-only scan */
 	so->indexTupDesc = scan->xs_itupdesc = RelationGetDescr(rel);
 
+	if (scan->numberOfOrderBys > 0)
+	{
+		so->zeroDistances = palloc(sizeof(double) * scan->numberOfOrderBys);
+		so->infDistances = palloc(sizeof(double) * scan->numberOfOrderBys);
+
+		for (i = 0; i < scan->numberOfOrderBys; i++)
+		{
+			so->zeroDistances[i] = 0.0;
+			so->infDistances[i] = get_float8_infinity();
+		}
+
+		scan->xs_orderbyvals = palloc0(sizeof(Datum) * scan->numberOfOrderBys);
+		scan->xs_orderbynulls = palloc(sizeof(bool) * scan->numberOfOrderBys);
+		memset(scan->xs_orderbynulls, true, sizeof(bool) * scan->numberOfOrderBys);
+	}
+
+	so->queueCxt = AllocSetContextCreate(CurrentMemoryContext,
+										 "SP-GiST queue context",
+										 ALLOCSET_DEFAULT_SIZES);
+
+	fmgr_info_copy(&so->innerConsistentFn,
+				   index_getprocinfo(rel, 1, SPGIST_INNER_CONSISTENT_PROC),
+				   CurrentMemoryContext);
+
+	fmgr_info_copy(&so->leafConsistentFn,
+				   index_getprocinfo(rel, 1, SPGIST_LEAF_CONSISTENT_PROC),
+				   CurrentMemoryContext);
+
+	so->indexCollation = rel->rd_indcollation[0];
+
 	scan->opaque = so;
 
 	return scan;
@@ -208,18 +282,51 @@ spgrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
 		  ScanKey orderbys, int norderbys)
 {
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
+	MemoryContext oldCxt;
 
 	/* copy scankeys into local storage */
 	if (scankey && scan->numberOfKeys > 0)
-	{
 		memmove(scan->keyData, scankey,
 				scan->numberOfKeys * sizeof(ScanKeyData));
+
+	if (orderbys && scan->numberOfOrderBys > 0)
+	{
+		int			i;
+
+		memmove(scan->orderByData, orderbys,
+				scan->numberOfOrderBys * sizeof(ScanKeyData));
+
+		so->orderByTypes = (Oid *) palloc(sizeof(Oid) * scan->numberOfOrderBys);
+
+		for (i = 0; i < scan->numberOfOrderBys; i++)
+		{
+			ScanKey		skey = &scan->orderByData[i];
+
+			/*
+			 * Look up the datatype returned by the original ordering
+			 * operator. SP-GiST always uses a float8 for the distance function,
+			 * but the ordering operator could be anything else.
+			 *
+			 * XXX: The distance function is only allowed to be lossy if the
+			 * ordering operator's result type is float4 or float8.  Otherwise
+			 * we don't know how to return the distance to the executor.  But
+			 * we cannot check that here, as we won't know if the distance
+			 * function is lossy until it returns *recheck = true for the
+			 * first time.
+			 */
+			so->orderByTypes[i] = get_func_rettype(skey->sk_func.fn_oid);
+		}
 	}
 
 	/* preprocess scankeys, set up the representation in *so */
 	spgPrepareScanKeys(scan);
 
-	/* set up starting stack entries */
+	MemoryContextReset(so->queueCxt);
+	oldCxt = MemoryContextSwitchTo(so->queueCxt);
+	so->queue = pairingheap_allocate(pairingheap_SpGistSearchItem_cmp, scan);
+	MemoryContextSwitchTo(oldCxt);
+
+	/* set up starting queue entries */
 	resetSpGistScanOpaque(so);
 }
 
@@ -229,65 +336,336 @@ spgendscan(IndexScanDesc scan)
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
 	MemoryContextDelete(so->tempCxt);
+	MemoryContextDelete(so->queueCxt);
+
+	if (scan->numberOfOrderBys > 0)
+	{
+		pfree(so->zeroDistances);
+		pfree(so->infDistances);
+	}
+}
+
+/*
+ * Leaf SpGistSearchItem constructor, called in queue context
+ */
+static SpGistSearchItem *
+spgNewHeapItem(SpGistScanOpaque so, int level, ItemPointerData heapPtr,
+			   Datum leafValue, bool recheckQual, bool recheckDist, bool isnull)
+{
+	SpGistSearchItem *item = (SpGistSearchItem *) palloc(
+								SizeOfSpGistSearchItem(so->numberOfOrderBys));
+
+	item->level = level;
+	item->heap = heapPtr;
+	/* copy value to queue cxt out of tmp cxt */
+	item->value = isnull ? (Datum) 0 :
+		datumCopy(leafValue, so->state.attType.attbyval,
+				  so->state.attType.attlen);
+	item->traversalValue = NULL;
+	item->isLeaf = true;
+	item->recheckQual = recheckQual;
+	item->recheckDist = recheckDist;
+	item->isnull = isnull;
+
+	return item;
 }
 
 /*
  * Test whether a leaf tuple satisfies all the scan keys
  *
- * *leafValue is set to the reconstructed datum, if provided
- * *recheck is set true if any of the operators are lossy
+ * *reportedSome is set to true if:
+ *		the scan is not ordered AND the item satisfies the scankeys
  */
 static bool
-spgLeafTest(Relation index, SpGistScanOpaque so,
+spgLeafTest(SpGistScanOpaque so, SpGistSearchItem *item,
 			SpGistLeafTuple leafTuple, bool isnull,
-			int level, Datum reconstructedValue,
-			void *traversalValue,
-			Datum *leafValue, bool *recheck)
+			bool *reportedSome, storeRes_func storeRes)
 {
+	Datum		leafValue;
+	double	   *distances;
 	bool		result;
-	Datum		leafDatum;
-	spgLeafConsistentIn in;
-	spgLeafConsistentOut out;
-	FmgrInfo   *procinfo;
-	MemoryContext oldCtx;
+	bool		recheckQual;
+	bool		recheckDist;
 
 	if (isnull)
 	{
 		/* Should not have arrived on a nulls page unless nulls are wanted */
 		Assert(so->searchNulls);
-		*leafValue = (Datum) 0;
-		*recheck = false;
-		return true;
+		leafValue = (Datum) 0;
+		/* Assume that all distances for null entries are infinities */
+		distances = so->infDistances;
+		recheckQual = false;
+		recheckDist = false;
+		result = true;
+	}
+	else
+	{
+		spgLeafConsistentIn in;
+		spgLeafConsistentOut out;
+
+		/* use temp context for calling leaf_consistent */
+		MemoryContext oldCxt = MemoryContextSwitchTo(so->tempCxt);
+
+		in.scankeys = so->keyData;
+		in.nkeys = so->numberOfKeys;
+		in.orderbykeys = so->orderByData;
+		in.norderbys = so->numberOfOrderBys;
+		in.reconstructedValue = item->value;
+		in.traversalValue = item->traversalValue;
+		in.level = item->level;
+		in.returnData = so->want_itup;
+		in.leafDatum = SGLTDATUM(leafTuple, &so->state);
+
+		out.leafValue = (Datum) 0;
+		out.recheck = false;
+		out.distances = NULL;
+		out.recheckDistances = false;
+
+		result = DatumGetBool(FunctionCall2Coll(&so->leafConsistentFn,
+												so->indexCollation,
+												PointerGetDatum(&in),
+												PointerGetDatum(&out)));
+		recheckQual = out.recheck;
+		recheckDist = out.recheckDistances;
+		leafValue = out.leafValue;
+		distances = out.distances;
+
+		MemoryContextSwitchTo(oldCxt);
 	}
 
-	leafDatum = SGLTDATUM(leafTuple, &so->state);
+	if (result)
+	{
+		/* item passes the scankeys */
+		if (so->numberOfOrderBys > 0)
+		{
+			/* the scan is ordered -> add the item to the queue */
+			MemoryContext oldCxt = MemoryContextSwitchTo(so->queueCxt);
+			SpGistSearchItem *heapItem = spgNewHeapItem(so, item->level,
+														leafTuple->heapPtr,
+														leafValue,
+														recheckQual,
+														recheckDist,
+														isnull);
+
+			spgAddSearchItemToQueue(so, heapItem, distances);
+
+			MemoryContextSwitchTo(oldCxt);
+		}
+		else
+		{
+			/* non-ordered scan, so report the item right away */
+			Assert(!recheckDist);
+			storeRes(so, &leafTuple->heapPtr, leafValue, isnull,
+					 recheckQual, false, NULL);
+			*reportedSome = true;
+		}
+	}
 
-	/* use temp context for calling leaf_consistent */
-	oldCtx = MemoryContextSwitchTo(so->tempCxt);
+	return result;
+}
 
-	in.scankeys = so->keyData;
-	in.nkeys = so->numberOfKeys;
-	in.reconstructedValue = reconstructedValue;
-	in.traversalValue = traversalValue;
-	in.level = level;
-	in.returnData = so->want_itup;
-	in.leafDatum = leafDatum;
+/* A bundle initializer for inner_consistent methods */
+static void
+spgInitInnerConsistentIn(spgInnerConsistentIn *in,
+						 SpGistScanOpaque so,
+						 SpGistSearchItem *item,
+						 SpGistInnerTuple innerTuple,
+						 MemoryContext traversalMemoryContext)
+{
+	in->scankeys = so->keyData;
+	in->nkeys = so->numberOfKeys;
+	in->norderbys = so->numberOfOrderBys;
+	in->orderbyKeys = so->orderByData;
+	in->reconstructedValue = item->value;
+	in->traversalMemoryContext = traversalMemoryContext;
+	in->traversalValue = item->traversalValue;
+	in->level = item->level;
+	in->returnData = so->want_itup;
+	in->allTheSame = innerTuple->allTheSame;
+	in->hasPrefix = (innerTuple->prefixSize > 0);
+	in->prefixDatum = SGITDATUM(innerTuple, &so->state);
+	in->nNodes = innerTuple->nNodes;
+	in->nodeLabels = spgExtractNodeLabels(&so->state, innerTuple);
+}
+
+static SpGistSearchItem *
+spgMakeInnerItem(SpGistScanOpaque so,
+				 SpGistSearchItem *parentItem,
+				 SpGistNodeTuple tuple,
+				 spgInnerConsistentOut *out, int i, bool isnull)
+{
+	SpGistSearchItem *item = palloc(SizeOfSpGistSearchItem(so->numberOfOrderBys));
+
+	item->heap = tuple->t_tid;
+	item->level = out->levelAdds ? parentItem->level + out->levelAdds[i]
+								 : parentItem->level;
+
+	/* Must copy value out of temp context */
+	item->value = out->reconstructedValues
+					? datumCopy(out->reconstructedValues[i],
+								so->state.attType.attbyval,
+								so->state.attType.attlen)
+					: (Datum) 0;
+
+	/*
+	 * Elements of out.traversalValues should be allocated in
+	 * in.traversalMemoryContext, which is actually a long
+	 * lived context of index scan.
+	 */
+	item->traversalValue =
+			out->traversalValues ? out->traversalValues[i] : NULL;
+
+	item->isLeaf = false;
+	item->recheckQual = false;
+	item->recheckDist = false;
+	item->isnull = isnull;
+
+	return item;
+}
 
-	out.leafValue = (Datum) 0;
-	out.recheck = false;
+static void
+spgInnerTest(SpGistScanOpaque so, SpGistSearchItem *item,
+			 SpGistInnerTuple innerTuple, bool isnull)
+{
+	MemoryContext			oldCxt = MemoryContextSwitchTo(so->tempCxt);
+	spgInnerConsistentOut	out;
+	int						nNodes = innerTuple->nNodes;
+	int						i;
 
-	procinfo = index_getprocinfo(index, 1, SPGIST_LEAF_CONSISTENT_PROC);
-	result = DatumGetBool(FunctionCall2Coll(procinfo,
-											index->rd_indcollation[0],
-											PointerGetDatum(&in),
-											PointerGetDatum(&out)));
+	memset(&out, 0, sizeof(out));
 
-	*leafValue = out.leafValue;
-	*recheck = out.recheck;
+	if (!isnull)
+	{
+		spgInnerConsistentIn in;
 
-	MemoryContextSwitchTo(oldCtx);
+		spgInitInnerConsistentIn(&in, so, item, innerTuple, oldCxt);
 
-	return result;
+		/* use user-defined inner consistent method */
+		FunctionCall2Coll(&so->innerConsistentFn,
+						  so->indexCollation,
+						  PointerGetDatum(&in),
+						  PointerGetDatum(&out));
+	}
+	else
+	{
+		/* force all children to be visited */
+		out.nNodes = nNodes;
+		out.nodeNumbers = (int *) palloc(sizeof(int) * nNodes);
+		for (i = 0; i < nNodes; i++)
+			out.nodeNumbers[i] = i;
+	}
+
+	/* If allTheSame, they should all or none of 'em match */
+	if (innerTuple->allTheSame)
+		if (out.nNodes != 0 && out.nNodes != nNodes)
+			elog(ERROR, "inconsistent inner_consistent results for allTheSame inner tuple");
+
+	if (out.nNodes)
+	{
+		/* collect node pointers */
+		SpGistNodeTuple		node;
+		SpGistNodeTuple	   *nodes = (SpGistNodeTuple *) palloc(
+									sizeof(SpGistNodeTuple) * nNodes);
+
+		SGITITERATE(innerTuple, i, node)
+		{
+			nodes[i] = node;
+		}
+
+		MemoryContextSwitchTo(so->queueCxt);
+
+		for (i = 0; i < out.nNodes; i++)
+		{
+			int			nodeN = out.nodeNumbers[i];
+			SpGistSearchItem *innerItem;
+
+			Assert(nodeN >= 0 && nodeN < nNodes);
+
+			node = nodes[nodeN];
+
+			if (!ItemPointerIsValid(&node->t_tid))
+				continue;
+
+			innerItem = spgMakeInnerItem(so, item, node, &out, i, isnull);
+
+			/* Will copy out the distances in spgAddSearchItemToQueue anyway */
+			spgAddSearchItemToQueue(so, innerItem,
+									out.distances ? out.distances[i]
+												  : so->infDistances);
+		}
+	}
+
+	MemoryContextSwitchTo(oldCxt);
+}
+
+/* Returns a next item in an (ordered) scan or null if the index is exhausted */
+static SpGistSearchItem *
+spgGetNextQueueItem(SpGistScanOpaque so)
+{
+	SpGistSearchItem *item;
+
+	if (!pairingheap_is_empty(so->queue))
+		item = (SpGistSearchItem *) pairingheap_remove_first(so->queue);
+	else
+		/* Done when both heaps are empty */
+		item = NULL;
+
+	/* Return item; caller is responsible to pfree it */
+	return item;
+}
+
+enum SpGistSpecialOffsetNumbers
+{
+	SpGistBreakOffsetNumber = InvalidOffsetNumber,
+	SpGistRedirectOffsetNumber = MaxOffsetNumber + 1,
+	SpGistErrorOffsetNumber = MaxOffsetNumber + 2
+};
+
+static OffsetNumber
+spgTestLeafTuple(SpGistScanOpaque so,
+				 SpGistSearchItem *item,
+				 Page page, OffsetNumber offset,
+				 bool isnull, bool isroot,
+				 bool *reportedSome,
+				 storeRes_func storeRes)
+{
+	SpGistLeafTuple leafTuple = (SpGistLeafTuple)
+		PageGetItem(page, PageGetItemId(page, offset));
+
+	if (leafTuple->tupstate != SPGIST_LIVE)
+	{
+		if (!isroot) /* all tuples on root should be live */
+		{
+			if (leafTuple->tupstate == SPGIST_REDIRECT)
+			{
+				/* redirection tuple should be first in chain */
+				Assert(offset == ItemPointerGetOffsetNumber(&item->heap));
+				/* transfer attention to redirect point */
+				item->heap = ((SpGistDeadTuple) leafTuple)->pointer;
+				Assert(ItemPointerGetBlockNumber(&item->heap) != SPGIST_METAPAGE_BLKNO);
+				return SpGistRedirectOffsetNumber;
+			}
+
+			if (leafTuple->tupstate == SPGIST_DEAD)
+			{
+				/* dead tuple should be first in chain */
+				Assert(offset == ItemPointerGetOffsetNumber(&item->heap));
+				/* No live entries on this page */
+				Assert(leafTuple->nextOffset == InvalidOffsetNumber);
+				return SpGistBreakOffsetNumber;
+			}
+		}
+
+		/* We should not arrive at a placeholder */
+		elog(ERROR, "unexpected SPGiST tuple state: %d", leafTuple->tupstate);
+		return SpGistErrorOffsetNumber;
+	}
+
+	Assert(ItemPointerIsValid(&leafTuple->heapPtr));
+
+	spgLeafTest(so, item, leafTuple, isnull, reportedSome, storeRes);
+
+	return leafTuple->nextOffset;
 }
 
 /*
@@ -306,247 +684,101 @@ spgWalk(Relation index, SpGistScanOpaque so, bool scanWholeIndex,
 
 	while (scanWholeIndex || !reportedSome)
 	{
-		ScanStackEntry *stackEntry;
-		BlockNumber blkno;
-		OffsetNumber offset;
-		Page		page;
-		bool		isnull;
+		SpGistSearchItem *item = spgGetNextQueueItem(so);
 
-		/* Pull next to-do item from the list */
-		if (so->scanStack == NIL)
-			break;				/* there are no more pages to scan */
-
-		stackEntry = (ScanStackEntry *) linitial(so->scanStack);
-		so->scanStack = list_delete_first(so->scanStack);
+		if (item == NULL)
+			break; /* No more items in queue -> done */
 
 redirect:
 		/* Check for interrupts, just in case of infinite loop */
 		CHECK_FOR_INTERRUPTS();
 
-		blkno = ItemPointerGetBlockNumber(&stackEntry->ptr);
-		offset = ItemPointerGetOffsetNumber(&stackEntry->ptr);
-
-		if (buffer == InvalidBuffer)
+		if (item->isLeaf)
 		{
-			buffer = ReadBuffer(index, blkno);
-			LockBuffer(buffer, BUFFER_LOCK_SHARE);
+			/* We store heap items in the queue only in case of ordered search */
+			Assert(so->numberOfOrderBys > 0);
+			storeRes(so, &item->heap, item->value, item->isnull,
+					 item->recheckQual, item->recheckDist, item->distances);
+			reportedSome = true;
 		}
-		else if (blkno != BufferGetBlockNumber(buffer))
+		else
 		{
-			UnlockReleaseBuffer(buffer);
-			buffer = ReadBuffer(index, blkno);
-			LockBuffer(buffer, BUFFER_LOCK_SHARE);
-		}
-		/* else new pointer points to the same page, no work needed */
+			BlockNumber		blkno  = ItemPointerGetBlockNumber(&item->heap);
+			OffsetNumber	offset = ItemPointerGetOffsetNumber(&item->heap);
+			Page			page;
+			bool			isnull;
 
-		page = BufferGetPage(buffer);
-		TestForOldSnapshot(snapshot, index, page);
+			if (buffer == InvalidBuffer)
+			{
+				buffer = ReadBuffer(index, blkno);
+				LockBuffer(buffer, BUFFER_LOCK_SHARE);
+			}
+			else if (blkno != BufferGetBlockNumber(buffer))
+			{
+				UnlockReleaseBuffer(buffer);
+				buffer = ReadBuffer(index, blkno);
+				LockBuffer(buffer, BUFFER_LOCK_SHARE);
+			}
 
-		isnull = SpGistPageStoresNulls(page) ? true : false;
+			/* else new pointer points to the same page, no work needed */
 
-		if (SpGistPageIsLeaf(page))
-		{
-			SpGistLeafTuple leafTuple;
-			OffsetNumber max = PageGetMaxOffsetNumber(page);
-			Datum		leafValue = (Datum) 0;
-			bool		recheck = false;
+			page = BufferGetPage(buffer);
+			TestForOldSnapshot(snapshot, index, page);
 
-			if (SpGistBlockIsRoot(blkno))
+			isnull = SpGistPageStoresNulls(page) ? true : false;
+
+			if (SpGistPageIsLeaf(page))
 			{
-				/* When root is a leaf, examine all its tuples */
-				for (offset = FirstOffsetNumber; offset <= max; offset++)
-				{
-					leafTuple = (SpGistLeafTuple)
-						PageGetItem(page, PageGetItemId(page, offset));
-					if (leafTuple->tupstate != SPGIST_LIVE)
-					{
-						/* all tuples on root should be live */
-						elog(ERROR, "unexpected SPGiST tuple state: %d",
-							 leafTuple->tupstate);
-					}
+				/* Page is a leaf - that is, all it's tuples are heap items */
+				OffsetNumber max = PageGetMaxOffsetNumber(page);
 
-					Assert(ItemPointerIsValid(&leafTuple->heapPtr));
-					if (spgLeafTest(index, so,
-									leafTuple, isnull,
-									stackEntry->level,
-									stackEntry->reconstructedValue,
-									stackEntry->traversalValue,
-									&leafValue,
-									&recheck))
-					{
-						storeRes(so, &leafTuple->heapPtr,
-								 leafValue, isnull, recheck);
-						reportedSome = true;
-					}
+				if (SpGistBlockIsRoot(blkno))
+				{
+					/* When root is a leaf, examine all its tuples */
+					for (offset = FirstOffsetNumber; offset <= max; offset++)
+						(void) spgTestLeafTuple(so, item, page, offset,
+												isnull, true,
+												&reportedSome, storeRes);
 				}
-			}
-			else
-			{
-				/* Normal case: just examine the chain we arrived at */
-				while (offset != InvalidOffsetNumber)
+				else
 				{
-					Assert(offset >= FirstOffsetNumber && offset <= max);
-					leafTuple = (SpGistLeafTuple)
-						PageGetItem(page, PageGetItemId(page, offset));
-					if (leafTuple->tupstate != SPGIST_LIVE)
+					/* Normal case: just examine the chain we arrived at */
+					while (offset != InvalidOffsetNumber)
 					{
-						if (leafTuple->tupstate == SPGIST_REDIRECT)
-						{
-							/* redirection tuple should be first in chain */
-							Assert(offset == ItemPointerGetOffsetNumber(&stackEntry->ptr));
-							/* transfer attention to redirect point */
-							stackEntry->ptr = ((SpGistDeadTuple) leafTuple)->pointer;
-							Assert(ItemPointerGetBlockNumber(&stackEntry->ptr) != SPGIST_METAPAGE_BLKNO);
+						Assert(offset >= FirstOffsetNumber && offset <= max);
+						offset = spgTestLeafTuple(so, item, page, offset,
+												  isnull, false,
+												  &reportedSome, storeRes);
+						if (offset == SpGistRedirectOffsetNumber)
 							goto redirect;
-						}
-						if (leafTuple->tupstate == SPGIST_DEAD)
-						{
-							/* dead tuple should be first in chain */
-							Assert(offset == ItemPointerGetOffsetNumber(&stackEntry->ptr));
-							/* No live entries on this page */
-							Assert(leafTuple->nextOffset == InvalidOffsetNumber);
-							break;
-						}
-						/* We should not arrive at a placeholder */
-						elog(ERROR, "unexpected SPGiST tuple state: %d",
-							 leafTuple->tupstate);
-					}
-
-					Assert(ItemPointerIsValid(&leafTuple->heapPtr));
-					if (spgLeafTest(index, so,
-									leafTuple, isnull,
-									stackEntry->level,
-									stackEntry->reconstructedValue,
-									stackEntry->traversalValue,
-									&leafValue,
-									&recheck))
-					{
-						storeRes(so, &leafTuple->heapPtr,
-								 leafValue, isnull, recheck);
-						reportedSome = true;
 					}
-
-					offset = leafTuple->nextOffset;
-				}
-			}
-		}
-		else	/* page is inner */
-		{
-			SpGistInnerTuple innerTuple;
-			spgInnerConsistentIn in;
-			spgInnerConsistentOut out;
-			FmgrInfo   *procinfo;
-			SpGistNodeTuple *nodes;
-			SpGistNodeTuple node;
-			int			i;
-			MemoryContext oldCtx;
-
-			innerTuple = (SpGistInnerTuple) PageGetItem(page,
-												PageGetItemId(page, offset));
-
-			if (innerTuple->tupstate != SPGIST_LIVE)
-			{
-				if (innerTuple->tupstate == SPGIST_REDIRECT)
-				{
-					/* transfer attention to redirect point */
-					stackEntry->ptr = ((SpGistDeadTuple) innerTuple)->pointer;
-					Assert(ItemPointerGetBlockNumber(&stackEntry->ptr) != SPGIST_METAPAGE_BLKNO);
-					goto redirect;
 				}
-				elog(ERROR, "unexpected SPGiST tuple state: %d",
-					 innerTuple->tupstate);
 			}
-
-			/* use temp context for calling inner_consistent */
-			oldCtx = MemoryContextSwitchTo(so->tempCxt);
-
-			in.scankeys = so->keyData;
-			in.nkeys = so->numberOfKeys;
-			in.reconstructedValue = stackEntry->reconstructedValue;
-			in.traversalMemoryContext = oldCtx;
-			in.traversalValue = stackEntry->traversalValue;
-			in.level = stackEntry->level;
-			in.returnData = so->want_itup;
-			in.allTheSame = innerTuple->allTheSame;
-			in.hasPrefix = (innerTuple->prefixSize > 0);
-			in.prefixDatum = SGITDATUM(innerTuple, &so->state);
-			in.nNodes = innerTuple->nNodes;
-			in.nodeLabels = spgExtractNodeLabels(&so->state, innerTuple);
-
-			/* collect node pointers */
-			nodes = (SpGistNodeTuple *) palloc(sizeof(SpGistNodeTuple) * in.nNodes);
-			SGITITERATE(innerTuple, i, node)
-			{
-				nodes[i] = node;
-			}
-
-			memset(&out, 0, sizeof(out));
-
-			if (!isnull)
+			else	/* page is inner */
 			{
-				/* use user-defined inner consistent method */
-				procinfo = index_getprocinfo(index, 1, SPGIST_INNER_CONSISTENT_PROC);
-				FunctionCall2Coll(procinfo,
-								  index->rd_indcollation[0],
-								  PointerGetDatum(&in),
-								  PointerGetDatum(&out));
-			}
-			else
-			{
-				/* force all children to be visited */
-				out.nNodes = in.nNodes;
-				out.nodeNumbers = (int *) palloc(sizeof(int) * in.nNodes);
-				for (i = 0; i < in.nNodes; i++)
-					out.nodeNumbers[i] = i;
-			}
-
-			MemoryContextSwitchTo(oldCtx);
-
-			/* If allTheSame, they should all or none of 'em match */
-			if (innerTuple->allTheSame)
-				if (out.nNodes != 0 && out.nNodes != in.nNodes)
-					elog(ERROR, "inconsistent inner_consistent results for allTheSame inner tuple");
-
-			for (i = 0; i < out.nNodes; i++)
-			{
-				int			nodeN = out.nodeNumbers[i];
+				SpGistInnerTuple innerTuple = (SpGistInnerTuple)
+						PageGetItem(page, PageGetItemId(page, offset));
 
-				Assert(nodeN >= 0 && nodeN < in.nNodes);
-				if (ItemPointerIsValid(&nodes[nodeN]->t_tid))
+				if (innerTuple->tupstate != SPGIST_LIVE)
 				{
-					ScanStackEntry *newEntry;
-
-					/* Create new work item for this node */
-					newEntry = palloc(sizeof(ScanStackEntry));
-					newEntry->ptr = nodes[nodeN]->t_tid;
-					if (out.levelAdds)
-						newEntry->level = stackEntry->level + out.levelAdds[i];
-					else
-						newEntry->level = stackEntry->level;
-					/* Must copy value out of temp context */
-					if (out.reconstructedValues)
-						newEntry->reconstructedValue =
-							datumCopy(out.reconstructedValues[i],
-									  so->state.attType.attbyval,
-									  so->state.attType.attlen);
-					else
-						newEntry->reconstructedValue = (Datum) 0;
-
-					/*
-					 * Elements of out.traversalValues should be allocated in
-					 * in.traversalMemoryContext, which is actually a long
-					 * lived context of index scan.
-					 */
-					newEntry->traversalValue = (out.traversalValues) ?
-						out.traversalValues[i] : NULL;
-
-					so->scanStack = lcons(newEntry, so->scanStack);
+					if (innerTuple->tupstate == SPGIST_REDIRECT)
+					{
+						/* transfer attention to redirect point */
+						item->heap = ((SpGistDeadTuple) innerTuple)->pointer;
+						Assert(ItemPointerGetBlockNumber(&item->heap) !=
+							   SPGIST_METAPAGE_BLKNO);
+						goto redirect;
+					}
+					elog(ERROR, "unexpected SPGiST tuple state: %d",
+						 innerTuple->tupstate);
 				}
+
+				spgInnerTest(so, item, innerTuple, isnull);
 			}
 		}
 
-		/* done with this scan stack entry */
-		freeScanStackEntry(so, stackEntry);
+		/* done with this scan item */
+		spgFreeSearchItem(so, item);
 		/* clear temp context before proceeding to the next one */
 		MemoryContextReset(so->tempCxt);
 	}
@@ -555,11 +787,14 @@ redirect:
 		UnlockReleaseBuffer(buffer);
 }
 
+
 /* storeRes subroutine for getbitmap case */
 static void
 storeBitmap(SpGistScanOpaque so, ItemPointer heapPtr,
-			Datum leafValue, bool isnull, bool recheck)
+			Datum leafValue, bool isnull, bool recheck, bool recheckDist,
+			double *distances)
 {
+	Assert(!recheckDist && !distances);
 	tbm_add_tuples(so->tbm, heapPtr, 1, recheck);
 	so->ntids++;
 }
@@ -583,11 +818,21 @@ spggetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
 /* storeRes subroutine for gettuple case */
 static void
 storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,
-			  Datum leafValue, bool isnull, bool recheck)
+			  Datum leafValue, bool isnull, bool recheck, bool recheckDist,
+			  double *distances)
 {
 	Assert(so->nPtrs < MaxIndexTuplesPerPage);
 	so->heapPtrs[so->nPtrs] = *heapPtr;
 	so->recheck[so->nPtrs] = recheck;
+	so->recheckDist[so->nPtrs] = recheckDist;
+
+	if (so->numberOfOrderBys > 0)
+	{
+		Size		size = sizeof(double) * so->numberOfOrderBys;
+
+		so->distances[so->nPtrs] = memcpy(palloc(size), distances, size);
+	}
+
 	if (so->want_itup)
 	{
 		/*
@@ -616,14 +861,28 @@ spggettuple(IndexScanDesc scan, ScanDirection dir)
 	{
 		if (so->iPtr < so->nPtrs)
 		{
-			/* continuing to return tuples from a leaf page */
+			/* continuing to return reported tuples */
 			scan->xs_ctup.t_self = so->heapPtrs[so->iPtr];
 			scan->xs_recheck = so->recheck[so->iPtr];
 			scan->xs_itup = so->indexTups[so->iPtr];
+
+			if (so->numberOfOrderBys > 0)
+				index_store_orderby_distances(scan, so->orderByTypes,
+											  so->distances[so->iPtr],
+											  so->recheckDist[so->iPtr]);
 			so->iPtr++;
 			return true;
 		}
 
+		if (so->numberOfOrderBys > 0)
+		{
+			/* Must pfree distances to avoid memory leak */
+			int			i;
+
+			for (i = 0; i < so->nPtrs; i++)
+				pfree(so->distances[i]);
+		}
+
 		if (so->want_itup)
 		{
 			/* Must pfree IndexTuples to avoid memory leak */
diff --git a/src/backend/access/spgist/spgtextproc.c b/src/backend/access/spgist/spgtextproc.c
index 8678854..00eb27f 100644
--- a/src/backend/access/spgist/spgtextproc.c
+++ b/src/backend/access/spgist/spgtextproc.c
@@ -86,6 +86,7 @@ spg_text_config(PG_FUNCTION_ARGS)
 	cfg->labelType = INT2OID;
 	cfg->canReturnData = true;
 	cfg->longValuesOK = true;	/* suffixing will shorten long values */
+	cfg->suppLen = 0; /* we don't need any supplimentary data */
 	PG_RETURN_VOID();
 }
 
diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index ca4b0bd..bcefa14 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -15,16 +15,21 @@
 
 #include "postgres.h"
 
+#include "access/amvalidate.h"
+#include "access/htup_details.h"
 #include "access/reloptions.h"
 #include "access/spgist_private.h"
 #include "access/transam.h"
 #include "access/xact.h"
+#include "catalog/pg_amop.h"
 #include "storage/bufmgr.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
 #include "utils/builtins.h"
+#include "utils/catcache.h"
 #include "utils/index_selfuncs.h"
 #include "utils/lsyscache.h"
+#include "utils/syscache.h"
 
 
 /*
@@ -39,7 +44,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->amstrategies = 0;
 	amroutine->amsupport = SPGISTNProc;
 	amroutine->amcanorder = false;
-	amroutine->amcanorderbyop = false;
+	amroutine->amcanorderbyop = true;
 	amroutine->amcanbackward = false;
 	amroutine->amcanunique = false;
 	amroutine->amcanmulticol = false;
@@ -59,7 +64,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->amcanreturn = spgcanreturn;
 	amroutine->amcostestimate = spgcostestimate;
 	amroutine->amoptions = spgoptions;
-	amroutine->amproperty = NULL;
+	amroutine->amproperty = spgproperty;
 	amroutine->amvalidate = spgvalidate;
 	amroutine->ambeginscan = spgbeginscan;
 	amroutine->amrescan = spgrescan;
@@ -907,3 +912,82 @@ SpGistPageAddNewItem(SpGistState *state, Page page, Item item, Size size,
 
 	return offnum;
 }
+
+/*
+ *	spgproperty() -- Check boolean properties of indexes.
+ *
+ * This is optional for most AMs, but is required for SP-GiST because the core
+ * property code doesn't support AMPROP_DISTANCE_ORDERABLE.
+ */
+bool
+spgproperty(Oid index_oid, int attno,
+			IndexAMProperty prop, const char *propname,
+			bool *res, bool *isnull)
+{
+	Oid			opclass,
+				opfamily,
+				opcintype;
+	CatCList   *catlist;
+	int			i;
+
+	/* Only answer column-level inquiries */
+	if (attno == 0)
+		return false;
+
+	switch (prop)
+	{
+		case AMPROP_DISTANCE_ORDERABLE:
+			break;
+		default:
+			return false;
+	}
+
+	/*
+	 * Currently, SP-GiST distance-ordered scans require that there be a
+	 * distance operator in the opclass with the default types. So we assume
+	 * that if such a operator exists, then there's a reason for it.
+	 */
+
+	/* First we need to know the column's opclass. */
+	opclass = get_index_column_opclass(index_oid, attno);
+	if (!OidIsValid(opclass))
+	{
+		*isnull = true;
+		return true;
+	}
+
+	/* Now look up the opclass family and input datatype. */
+	if (!get_opclass_opfamily_and_input_type(opclass, &opfamily, &opcintype))
+	{
+		*isnull = true;
+		return true;
+	}
+
+	/* And now we can check whether the operator is provided. */
+	catlist = SearchSysCacheList1(AMOPSTRATEGY,
+								  ObjectIdGetDatum(opfamily));
+
+	*res = false;
+
+	for (i = 0; i < catlist->n_members; i++)
+	{
+		HeapTuple	amoptup = &catlist->members[i]->tuple;
+		Form_pg_amop amopform = (Form_pg_amop) GETSTRUCT(amoptup);
+
+		if (amopform->amoppurpose == AMOP_ORDER &&
+			(amopform->amoplefttype == opcintype ||
+			 amopform->amoprighttype == opcintype) &&
+			 opfamily_can_sort_type(amopform->amopsortfamily,
+									get_op_rettype(amopform->amopopr)))
+		{
+			*res = true;
+			break;
+		}
+	}
+
+	ReleaseSysCacheList(catlist);
+
+	*isnull = false;
+
+	return true;
+}
diff --git a/src/backend/access/spgist/spgvalidate.c b/src/backend/access/spgist/spgvalidate.c
index 1bc5bce..0a3eeb6 100644
--- a/src/backend/access/spgist/spgvalidate.c
+++ b/src/backend/access/spgist/spgvalidate.c
@@ -22,6 +22,7 @@
 #include "catalog/pg_opfamily.h"
 #include "catalog/pg_type.h"
 #include "utils/builtins.h"
+#include "utils/lsyscache.h"
 #include "utils/regproc.h"
 #include "utils/syscache.h"
 
@@ -138,6 +139,7 @@ spgvalidate(Oid opclassoid)
 	{
 		HeapTuple	oprtup = &oprlist->members[i]->tuple;
 		Form_pg_amop oprform = (Form_pg_amop) GETSTRUCT(oprtup);
+		Oid			op_rettype;
 
 		/* TODO: Check that only allowed strategy numbers exist */
 		if (oprform->amopstrategy < 1 || oprform->amopstrategy > 63)
@@ -151,20 +153,26 @@ spgvalidate(Oid opclassoid)
 			result = false;
 		}
 
-		/* spgist doesn't support ORDER BY operators */
-		if (oprform->amoppurpose != AMOP_SEARCH ||
-			OidIsValid(oprform->amopsortfamily))
+		/* spgist supports ORDER BY operators */
+		if (oprform->amoppurpose != AMOP_SEARCH)
 		{
-			ereport(INFO,
-					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
-					 errmsg("spgist operator family \"%s\" contains invalid ORDER BY specification for operator %s",
-							opfamilyname,
-							format_operator(oprform->amopopr))));
-			result = false;
+			/* ... and operator result must match the claimed btree opfamily */
+			op_rettype = get_op_rettype(oprform->amopopr);
+			if (!opfamily_can_sort_type(oprform->amopsortfamily, op_rettype))
+			{
+				ereport(INFO,
+						(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+						 errmsg("spgist operator family %s contains incorrect ORDER BY opfamily specification for operator %s",
+								opfamilyname,
+								format_operator(oprform->amopopr))));
+				result = false;
+			}
 		}
+		else
+			op_rettype = BOOLOID;
 
 		/* Check operator signature --- same for all spgist strategies */
-		if (!check_amop_signature(oprform->amopopr, BOOLOID,
+		if (!check_amop_signature(oprform->amopopr, op_rettype,
 								  oprform->amoplefttype,
 								  oprform->amoprighttype))
 		{
diff --git a/src/include/access/spgist.h b/src/include/access/spgist.h
index aaf78bc..23ed9bb 100644
--- a/src/include/access/spgist.h
+++ b/src/include/access/spgist.h
@@ -133,7 +133,9 @@ typedef struct spgPickSplitOut
 typedef struct spgInnerConsistentIn
 {
 	ScanKey		scankeys;		/* array of operators and comparison values */
+	ScanKey		orderbyKeys;
 	int			nkeys;			/* length of array */
+	int			norderbys;
 
 	Datum		reconstructedValue;		/* value reconstructed at parent */
 	void	   *traversalValue; /* opclass-specific traverse value */
@@ -157,6 +159,7 @@ typedef struct spgInnerConsistentOut
 	int		   *levelAdds;		/* increment level by this much for each */
 	Datum	   *reconstructedValues;	/* associated reconstructed values */
 	void	  **traversalValues;	/* opclass-specific traverse values */
+	double	  **distances;		/* associated distances */
 } spgInnerConsistentOut;
 
 /*
@@ -165,7 +168,10 @@ typedef struct spgInnerConsistentOut
 typedef struct spgLeafConsistentIn
 {
 	ScanKey		scankeys;		/* array of operators and comparison values */
+	ScanKey		orderbykeys;	/* array of ordering operators and comparison
+								 * values */
 	int			nkeys;			/* length of array */
+	int			norderbys;
 
 	Datum		reconstructedValue;		/* value reconstructed at parent */
 	void	   *traversalValue; /* opclass-specific traverse value */
@@ -179,6 +185,8 @@ typedef struct spgLeafConsistentOut
 {
 	Datum		leafValue;		/* reconstructed original data, if any */
 	bool		recheck;		/* set true if operator must be rechecked */
+	bool		recheckDistances; /* set true if distances must be rechecked */
+	double	   *distances;		/* associated distances */
 } spgLeafConsistentOut;
 
 
diff --git a/src/include/access/spgist_private.h b/src/include/access/spgist_private.h
index b2979a9..14d0700 100644
--- a/src/include/access/spgist_private.h
+++ b/src/include/access/spgist_private.h
@@ -16,8 +16,10 @@
 
 #include "access/itup.h"
 #include "access/spgist.h"
+#include "lib/rbtree.h"
 #include "nodes/tidbitmap.h"
 #include "storage/buf.h"
+#include "storage/relfilenode.h"
 #include "utils/relcache.h"
 
 
@@ -129,12 +131,34 @@ typedef struct SpGistState
 	bool		isBuild;		/* true if doing index build */
 } SpGistState;
 
+typedef struct SpGistSearchItem
+{
+	pairingheap_node phNode;	/* pairing heap node */
+	Datum		value;			/* value reconstructed from parent or
+								 * leafValue if heaptuple */
+	void	   *traversalValue; /* opclass-specific traverse value */
+	int			level;			/* level of items on this page */
+	ItemPointerData heap;		/* heap info, if heap tuple */
+	bool		isLeaf;			/* SearchItem is heap item */
+	bool		recheckQual;	/* qual recheck is needed */
+	bool		recheckDist;	/* distance recheck is needed */
+	bool		isnull;
+
+	/* array with numberOfOrderBys entries */
+	double		distances[FLEXIBLE_ARRAY_MEMBER];
+} SpGistSearchItem;
+
+#define SizeOfSpGistSearchItem(n_distances) \
+	(offsetof(SpGistSearchItem, distances) + sizeof(double) * (n_distances))
+
 /*
  * Private state of an index scan
  */
 typedef struct SpGistScanOpaqueData
 {
 	SpGistState state;			/* see above */
+	pairingheap *queue;			/* queue of unvisited items */
+	MemoryContext queueCxt;		/* context holding the queue */
 	MemoryContext tempCxt;		/* short-lived memory context */
 
 	/* Control flags showing whether to search nulls and/or non-nulls */
@@ -144,9 +168,17 @@ typedef struct SpGistScanOpaqueData
 	/* Index quals to be passed to opclass (null-related quals removed) */
 	int			numberOfKeys;	/* number of index qualifier conditions */
 	ScanKey		keyData;		/* array of index qualifier descriptors */
+	int			numberOfOrderBys;
+	ScanKey		orderByData;
+	Oid		   *orderByTypes;
+
+	FmgrInfo	innerConsistentFn;
+	FmgrInfo	leafConsistentFn;
+	Oid			indexCollation;
 
-	/* Stack of yet-to-be-visited pages */
-	List	   *scanStack;		/* List of ScanStackEntrys */
+	/* Pre-allocated workspace arrays: */
+	double	   *zeroDistances;
+	double	   *infDistances;
 
 	/* These fields are only used in amgetbitmap scans: */
 	TIDBitmap  *tbm;			/* bitmap being filled */
@@ -159,7 +191,9 @@ typedef struct SpGistScanOpaqueData
 	int			iPtr;			/* index for scanning through same */
 	ItemPointerData heapPtrs[MaxIndexTuplesPerPage];	/* TIDs from cur page */
 	bool		recheck[MaxIndexTuplesPerPage]; /* their recheck flags */
+	bool		recheckDist[MaxIndexTuplesPerPage]; /* distance recheck flags */
 	IndexTuple	indexTups[MaxIndexTuplesPerPage];		/* reconstructed tuples */
+	double	   *distances[MaxIndexTuplesPerPage];	/* distances (for recheck) */
 
 	/*
 	 * Note: using MaxIndexTuplesPerPage above is a bit hokey since
@@ -637,6 +671,9 @@ extern OffsetNumber SpGistPageAddNewItem(SpGistState *state, Page page,
 					 Item item, Size size,
 					 OffsetNumber *startOffset,
 					 bool errorOK);
+extern bool spgproperty(Oid index_oid, int attno,
+			IndexAMProperty prop, const char *propname,
+			bool *res, bool *isnull);
 
 /* spgdoinsert.c */
 extern void spgUpdateNodeLink(SpGistInnerTuple tup, int nodeN,