Fix pgstatindex() to give consistent results for empty indexes.

For an empty index, the pgstatindex() function would compute 0.0/0.0 for
its avg_leaf_density and leaf_fragmentation outputs.  On machines that
follow the IEEE float arithmetic standard with any care, that results in
a NaN.  However, per report from Rushabh Lathia, Microsoft couldn't
manage to get this right, so you'd get a bizarre error on Windows.

Fix by forcing the results to be NaN explicitly, rather than relying on
the division operator to give that or the snprintf function to print it
correctly.  I have some doubts that this is really the most useful
definition, but it seems better to remain backward-compatible with
those platforms for which the behavior wasn't completely broken.

Back-patch to 8.2, since the code is like that in all current releases.

diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index fd2cc9246bcc57ac588c0c1646fa22cd315cc42b..0fc3ecff6a7406a4a8fc1ebe85b488fa36589c21 100644 (file)
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -234,9 +234,17 @@ pgstatindex(PG_FUNCTION_ARGS)
                values[j] = palloc(32);
                snprintf(values[j++], 32, INT64_FORMAT, indexStat.deleted_pages);
                values[j] = palloc(32);
-               snprintf(values[j++], 32, "%.2f", 100.0 - (double) indexStat.free_space / (double) indexStat.max_avail * 100.0);
+               if (indexStat.max_avail > 0)
+                       snprintf(values[j++], 32, "%.2f",
+                                        100.0 - (double) indexStat.free_space / (double) indexStat.max_avail * 100.0);
+               else
+                       snprintf(values[j++], 32, "NaN");
                values[j] = palloc(32);
-               snprintf(values[j++], 32, "%.2f", (double) indexStat.fragments / (double) indexStat.leaf_pages * 100.0);
+               if (indexStat.leaf_pages > 0)
+                       snprintf(values[j++], 32, "%.2f",
+                                        (double) indexStat.fragments / (double) indexStat.leaf_pages * 100.0);
+               else
+                       snprintf(values[j++], 32, "NaN");
 
                tuple = BuildTupleFromCStrings(TupleDescGetAttInMetadata(tupleDesc),
                                                                           values);