Fix handling Inf and Nan values in GiST pairing heap comparator

Previously plain float comparison was used in GiST pairing heap.  Such
comparison doesn't provide proper ordering for value sets containing Inf and Nan
values.  This commit fixes that by usage of float8_cmp_internal().  Note, there
is remaining problem with NULL distances, which are represented as Inf in
pairing heap.  It would be fixes in subsequent commit.

Backpatch to all supported versions.

Reported-by: Andrey Borodin
Discussion: https://postgr.es/m/CAPpHfdsNvNdA0DBS%2BwMpFrgwT6C3-q50sFVGLSiuWnV3FqOJuQ%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Heikki Linnakangas
Backpatch-through: 9.4

diff --git a/src/backend/access/gist/gistscan.c b/src/backend/access/gist/gistscan.c
index 058544e2ae24345f33545dfd82f76c2dd06083b7..f5d8a01fe5ae5fea38cd905f6c991332b315848a 100644 (file)
--- a/src/backend/access/gist/gistscan.c
+++ b/src/backend/access/gist/gistscan.c
@@ -17,6 +17,7 @@
 #include "access/gist_private.h"
 #include "access/gistscan.h"
 #include "access/relscan.h"
+#include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
@@ -36,8 +37,10 @@ pairingheap_GISTSearchItem_cmp(const pairingheap_node *a, const pairingheap_node
        /* 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;
+               int                     cmp = -float8_cmp_internal(sa->distances[i], sb->distances[i]);
+
+               if (cmp != 0)
+                       return cmp;
        }
 
        /* Heap items go before inner pages, to ensure a depth-first search */