Fix more confusion in SP-GiST.

tglsfdc · tglsfdc · commit dfc843d46568 · 2021-04-04T17:57:07.000-04:00
spg_box_quad_leaf_consistent unconditionally returned the leaf datum as leafValue, even though in its usage for poly_ops that value is of completely the wrong type. In versions before 12, that was harmless because the core code did nothing with leafValue in non-index-only scans ... but since commit 2a63683, if we were doing a KNN-style scan, spgNewHeapItem would unconditionally try to copy the value using the wrong datatype parameters. Said copying is a waste of time and space if we're not going to return the data, but it accidentally failed to fail until I fixed the datatype confusion in ac9099f. Hence, change spgNewHeapItem to not copy the datum unless we're actually going to return it later. This saves cycles and dodges the question of whether lossy opclasses are returning the right type. Also change spg_box_quad_leaf_consistent to not return data that might be of the wrong type, as insurance against somebody introducing a similar bug into the core code in future. It seems like a good idea to back-patch these two changes into v12 and v13, although I'm afraid to change spgNewHeapItem's mistaken idea of which datatype to use in those branches. Per buildfarm results from ac9099f. Discussion: https://postgr.es/m/3728741.1617381471@sss.pgh.pa.us
diff --git a/src/backend/access/spgist/spgscan.c b/src/backend/access/spgist/spgscan.c
@@ -463,11 +463,19 @@ spgNewHeapItem(SpGistScanOpaque so, int level, ItemPointer heapPtr,
 
 	item->level = level;
 	item->heapPtr = *heapPtr;
-	/* copy value to queue cxt out of tmp cxt */
-	/* caution: "leafValue" is of type attType not leafType */
-	item->value = isnull ? (Datum) 0 :
-		datumCopy(leafValue, so->state.attType.attbyval,
-				  so->state.attType.attlen);
+
+	/*
+	 * If we need the reconstructed value, copy it to queue cxt out of tmp
+	 * cxt.  Caution: the leaf_consistent method may not have supplied a value
+	 * if we didn't ask it to, and mildly-broken methods might supply one of
+	 * the wrong type.  The correct leafValue type is attType not leafType.
+	 */
+	if (so->want_itup)
+		item->value = isnull ? (Datum) 0 :
+			datumCopy(leafValue, so->state.attType.attbyval,
+					  so->state.attType.attlen);
+	else
+		item->value = (Datum) 0;
 	item->traversalValue = NULL;
 	item->isLeaf = true;
 	item->recheck = recheck;
diff --git a/src/backend/utils/adt/geo_spgist.c b/src/backend/utils/adt/geo_spgist.c
@@ -749,8 +749,13 @@ spg_box_quad_leaf_consistent(PG_FUNCTION_ARGS)
 	/* All tests are exact. */
 	out->recheck = false;
 
-	/* leafDatum is what it is... */
-	out->leafValue = in->leafDatum;
+	/*
+	 * Don't return leafValue unless told to; this is used for both box and
+	 * polygon opclasses, and in the latter case the leaf datum is not even of
+	 * the right type to return.
+	 */
+	if (in->returnData)
+		out->leafValue = leaf;
 
 	/* Perform the required comparison(s) */
 	for (i = 0; i < in->nkeys; i++)
