Fix multiple bugs in contrib/pgstattuple's pgstatindex() function.

Dead or half-dead index leaf pages were incorrectly reported as live, as a
consequence of a code rearrangement I made (during a moment of severe brain
fade, evidently) in commit d287818eb514d431.

The index metapage was not counted in index_size, causing that result to
not agree with the actual index size on-disk.

Index root pages were not counted in internal_pages, which is inconsistent
compared to the case of a root that's also a leaf (one-page index), where
the root would be counted in leaf_pages.  Aside from that inconsistency,
this could lead to additional transient discrepancies between the reported
page counts and index_size, since it's possible for pgstatindex's scan to
see zero or multiple pages marked as BTP_ROOT, if the root moves due to
a split during the scan.  With these fixes, index_size will always be
exactly one page more than the sum of the displayed page counts.

Also, the index_size result was incorrectly documented as being measured in
pages; it's always been measured in bytes.  (While fixing that, I couldn't
resist doing some small additional wordsmithing on the pgstattuple docs.)

Including the metapage causes the reported index_size to not be zero for
an empty index.  To preserve the desired property that the pgstattuple
regression test results are platform-independent (ie, BLCKSZ configuration
independent), scale the index_size result in the regression tests.

The documentation issue was reported by Otsuka Kenji, and the inconsistent
root page counting by Peter Geoghegan; the other problems noted by me.
Back-patch to all supported branches, because this has been broken for
a long time.

diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index ceabd862a86ea1caeec51b09be2440cfefa85353..0aa517a870a51fe7e01ad42c45ac7b05dd3462c5 100644 (file)
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -66,7 +66,6 @@ typedef struct BTIndexStat
        uint32          level;
        BlockNumber root_blkno;
 
-       uint64          root_pages;
        uint64          internal_pages;
        uint64          leaf_pages;
        uint64          empty_pages;
@@ -133,7 +132,6 @@ pgstatindex(PG_FUNCTION_ARGS)
        }
 
        /* -- init counters -- */
-       indexStat.root_pages = 0;
        indexStat.internal_pages = 0;
        indexStat.leaf_pages = 0;
        indexStat.empty_pages = 0;
@@ -166,7 +164,11 @@ pgstatindex(PG_FUNCTION_ARGS)
 
                /* Determine page type, and update totals */
 
-               if (P_ISLEAF(opaque))
+               if (P_ISDELETED(opaque))
+                       indexStat.deleted_pages++;
+               else if (P_IGNORE(opaque))
+                       indexStat.empty_pages++;        /* this is the "half dead" state */
+               else if (P_ISLEAF(opaque))
                {
                        int                     max_avail;
 
@@ -183,12 +185,6 @@ pgstatindex(PG_FUNCTION_ARGS)
                        if (opaque->btpo_next != P_NONE && opaque->btpo_next < blkno)
                                indexStat.fragments++;
                }
-               else if (P_ISDELETED(opaque))
-                       indexStat.deleted_pages++;
-               else if (P_IGNORE(opaque))
-                       indexStat.empty_pages++;
-               else if (P_ISROOT(opaque))
-                       indexStat.root_pages++;
                else
                        indexStat.internal_pages++;
 
@@ -220,7 +216,7 @@ pgstatindex(PG_FUNCTION_ARGS)
                snprintf(values[j++], 32, "%d", indexStat.level);
                values[j] = palloc(32);
                snprintf(values[j++], 32, INT64_FORMAT,
-                                (indexStat.root_pages +
+                                (1 +           /* include the metapage in index_size */
                                  indexStat.leaf_pages +
                                  indexStat.internal_pages +
                                  indexStat.deleted_pages +

diff --git a/doc/src/sgml/pgstattuple.sgml b/doc/src/sgml/pgstattuple.sgml
index a55b35cb3f1b0e49bbead372a537b02fe36455b1..7f1ae8d304868fb981e3f3ee8d68e2a08aaf1079 100644 (file)
--- a/doc/src/sgml/pgstattuple.sgml
+++ b/doc/src/sgml/pgstattuple.sgml
@@ -146,13 +146,13 @@ test=> SELECT * FROM pgstatindex('pg_cast_oid_index');
 -[ RECORD 1 ]------+------
 version            | 2
 tree_level         | 0
-index_size         | 8192
+index_size         | 16384
 root_block_no      | 1
 internal_pages     | 0
 leaf_pages         | 1
 empty_pages        | 0
 deleted_pages      | 0
-avg_leaf_density   | 50.27
+avg_leaf_density   | 54.27
 leaf_fragmentation | 0
 </programlisting>
      </para>
@@ -186,13 +186,13 @@ leaf_fragmentation | 0
        <row>
         <entry><structfield>index_size</structfield></entry>
         <entry><type>bigint</type></entry>
-        <entry>Total number of pages in index</entry>
+        <entry>Total index size in bytes</entry>
        </row>
 
        <row>
         <entry><structfield>root_block_no</structfield></entry>
         <entry><type>bigint</type></entry>
-        <entry>Location of root block</entry>
+        <entry>Location of root page (zero if none)</entry>
        </row>
 
        <row>
@@ -236,6 +236,13 @@ leaf_fragmentation | 0
     </informaltable>
     </para>
 
+    <para>
+     The reported <literal>index_size</> will normally correspond to one more
+     page than is accounted for by <literal>internal_pages + leaf_pages +
+     empty_pages + deleted_pages</literal>, because it also includes the
+     index's metapage.
+    </para>
+
     <para>
      As with <function>pgstattuple</>, the results are accumulated
      page-by-page, and should not be expected to represent an