Added comment [skip ci]

src/ivfflat.c

@@ -182,6 +182,15 @@ ivfflatvalidate(Oid opclassoid)
 	return true;
 }
 
+/*
+ * Checks if index-only scan is supported
+ */
+static bool
+ivfflatcanreturn(Relation index, int attno)
+{
+	return attno == 1 && IvfflatOptionalProcInfo(index, IVFFLAT_NORM_PROC) == NULL;
+}
+
 /*
  * Define index handler
  *
@@ -223,7 +232,7 @@ ivfflathandler(PG_FUNCTION_ARGS)
 	amroutine->aminsert = ivfflatinsert;
 	amroutine->ambulkdelete = ivfflatbulkdelete;
 	amroutine->amvacuumcleanup = ivfflatvacuumcleanup;
-	amroutine->amcanreturn = NULL;	/* tuple not included in heapsort */
+	amroutine->amcanreturn = ivfflatcanreturn;
 	amroutine->amcostestimate = ivfflatcostestimate;
 	amroutine->amoptions = ivfflatoptions;
 	amroutine->amproperty = NULL;	/* TODO AMPROP_DISTANCE_ORDERABLE */

src/ivfflat.h

@@ -248,6 +248,7 @@ typedef struct IvfflatScanOpaqueData
 	bool		first;
 	Buffer		buf;
 	ItemPointerData heaptid;
+	IndexTuple	itup;
 
 	/* Sorting */
 	Tuplesortstate *sortstate;

src/ivfscan.c

@@ -141,6 +141,7 @@ GetScanItems(IndexScanDesc scan, Datum value)
 				IndexTuple	itup;
 				Datum		datum;
 				bool		isnull;
+				ItemPointerData indextid;
 				ItemId		itemid = PageGetItemId(page, offno);
 
 				/* Skip dead tuples */
@@ -149,6 +150,7 @@ GetScanItems(IndexScanDesc scan, Datum value)
 
 				itup = (IndexTuple) PageGetItem(page, itemid);
 				datum = index_getattr(itup, 1, tupdesc, &isnull);
+				ItemPointerSet(&indextid, searchPage, offno);
 
 				/*
 				 * Add virtual tuple
@@ -161,7 +163,7 @@ GetScanItems(IndexScanDesc scan, Datum value)
 				slot->tts_isnull[0] = false;
 				slot->tts_values[1] = PointerGetDatum(&itup->t_tid);
 				slot->tts_isnull[1] = false;
-				slot->tts_values[2] = Int32GetDatum((int) searchPage);
+				slot->tts_values[2] = PointerGetDatum(&indextid);
 				slot->tts_isnull[2] = false;
 				ExecStoreVirtualTuple(slot);
 
@@ -236,6 +238,34 @@ MarkPriorTupleDead(IndexScanDesc scan)
 	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
 }
 
+/*
+ * Set tuple for index-only scan
+ */
+static void
+SetIndexTuple(IndexScanDesc scan, ItemPointer indextid)
+{
+	IvfflatScanOpaque so = (IvfflatScanOpaque) scan->opaque;
+	Buffer		buf = so->buf;
+	Page		page;
+	OffsetNumber offno = ItemPointerGetOffsetNumber(indextid);
+	IndexTuple	itup;
+	Size		itupSize;
+
+	LockBuffer(buf, BUFFER_LOCK_SHARE);
+	page = BufferGetPage(buf);
+	itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offno));
+	itupSize = IndexTupleSize(itup);
+
+	if (so->itup == NULL)
+		so->itup = palloc(BLCKSZ);
+
+	memcpy(so->itup, itup, itupSize);
+
+	scan->xs_itup = so->itup;
+
+	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+}
+
 /*
  * Prepare for an index scan
  */
@@ -264,6 +294,7 @@ ivfflatbeginscan(Relation index, int nkeys, int norderbys)
 	so->buf = InvalidBuffer;
 	so->first = true;
 	ItemPointerSetInvalid(&so->heaptid);
+	so->itup = NULL;
 	so->probes = probes;
 	so->dimensions = dimensions;
 
@@ -280,7 +311,7 @@ ivfflatbeginscan(Relation index, int nkeys, int norderbys)
 #endif
 	TupleDescInitEntry(so->tupdesc, (AttrNumber) 1, "distance", FLOAT8OID, -1, 0);
 	TupleDescInitEntry(so->tupdesc, (AttrNumber) 2, "heaptid", TIDOID, -1, 0);
-	TupleDescInitEntry(so->tupdesc, (AttrNumber) 3, "indexblkno", INT4OID, -1, 0);
+	TupleDescInitEntry(so->tupdesc, (AttrNumber) 3, "indextid", TIDOID, -1, 0);
 
 	/* Prep sort */
 	so->sortstate = tuplesort_begin_heap(so->tupdesc, 1, attNums, sortOperators, sortCollations, nullsFirstFlags, work_mem, NULL, false);
@@ -295,6 +326,8 @@ ivfflatbeginscan(Relation index, int nkeys, int norderbys)
 
 	scan->opaque = so;
 
+	scan->xs_itupdesc = RelationGetDescr(index);
+
 	return scan;
 }
 
@@ -380,7 +413,7 @@ ivfflatgettuple(IndexScanDesc scan, ScanDirection dir)
 	if (tuplesort_gettupleslot(so->sortstate, true, false, so->slot, NULL))
 	{
 		ItemPointer heaptid = (ItemPointer) DatumGetPointer(slot_getattr(so->slot, 2, &so->isnull));
-		BlockNumber indexblkno = DatumGetInt32(slot_getattr(so->slot, 3, &so->isnull));
+		ItemPointer indextid = (ItemPointer) DatumGetPointer(slot_getattr(so->slot, 3, &so->isnull));
 
 #if PG_VERSION_NUM >= 120000
 		scan->xs_heaptid = *heaptid;
@@ -401,7 +434,11 @@ ivfflatgettuple(IndexScanDesc scan, ScanDirection dir)
 		 *
 		 * https://www.postgresql.org/docs/current/index-locking.html
 		 */
-		so->buf = ReadBuffer(scan->indexRelation, indexblkno);
+		so->buf = ReadBuffer(scan->indexRelation, ItemPointerGetBlockNumber(indextid));
+
+		/* Set tuple for index-only scan */
+		if (scan->xs_want_itup)
+			SetIndexTuple(scan, indextid);
 
 		scan->xs_recheckorderby = false;
 		return true;
@@ -422,6 +459,9 @@ ivfflatendscan(IndexScanDesc scan)
 	if (BufferIsValid(so->buf))
 		ReleaseBuffer(so->buf);
 
+	if (so->itup != NULL)
+		pfree(so->itup);
+
 	pairingheap_free(so->listQueue);
 	tuplesort_end(so->sortstate);